Battle in the Center of the Mind

One of the basic building blocks of story telling is a character's inner struggle, their efforts to balance their base urges and lofty ideals. This is not conducive to high octane explosions and fist fights, nor is it easily transmitted in television even by serious series. However, toss in demons, Mind Control, and a Journey to the Center of the Mind, and you'll get a Battle in the Center of the Mind.

What ends up happening is you get the mental equivalent of a no-holds-barred psychic showdown between the evil force trying to take over and the owner or his allies. The evil force can be of various natures, including: Demons, Ghosts, an evil computer virus, other humans via Mind Control or the self with an Enemy Within or Super-Powered Evil Side. What the possessing force wants is either a full Split Personality Takeover, or (if external) to maintain control.

Opposing this force is usually the "host" or person that is being affected. Occasionally, their mind is too weak and addled to oppose the invader, so a friendly telepath or mystic will insert an ally or two to try and rout the bad guy. They will fail. However, the act of them trying and yelling "I know you are in there somewhere!" and going in to save them from the evil presence in their mind is usually enough to get the host to kick their unwanted guest out of their mind if not completely obliterate it when it threatens their friends. The thing is, no matter how powerful the invader, it can't beat a determined victim's home field brain advantage.

The fight itself will usually use highly symbolic weapons (a chef's ladle now doubles as a BFS), defenses (a security blanket can now block Ki Attacks) and even imaginary allies (summoning up an army of Supermen to help you out), turning into something similar to a Shapeshifter Showdown.

For those on the outside, it's usually obvious that the character is Fighting From the Inside.

Anime & Manga

 * Keima Katsuragi has some of the most extreme (and funny) wars in his head over various video game related subjects. One involved a enormous space war complete with Mobile Suit Gundam and Star Wars references, fought by armies of himself. Though it's probably his imagination.
 * Magical Project S
 * Bleach—Ichigo vs Hollow Ichigo. In the anime it's fleshed out a bit more, making him re-experience his fights with Kenpachi, Byakuya and Jin Kariya before fighting Hichigo.
 * And now Ichigo's getting another one with
 * And it looks like
 * Mahou Sensei Negima has Negi fighting Evangeline (or at least a being created from his memories of her) inside his own head as part of his test for learning Black Magic.
 * Done backwards in Martian Successor Nadesico when Akito engages in a virtual battle with the ship's computer to delete its memories. In this case deleting the computer's memories was the heroic thing to do, but the computer wasn't aware of this and fought to protect itself. Both Akito and the computer chose to virtually represent themselves as Gekigangar III, the titular giant robot from Nadesico's Show Within a Show, combining this trope with Fearful Symmetry.
 * Crops up in Paranoia Agent; Or is it a Lotus Eater Machine?
 * Happens between brother and sister Masamune and Tsubaki Nakatsukasa in Soul Eater. The conflict between the two souls (Masamune being able to possess Tsubaki, which she allowed in order to confront him) is shown as a physical battle between the two, each using their own weapon forms. Souls get Mental Worlds elsewhere in the series, but this is the only actual battle so far. Curiously, Black Star's attempt at mastering the form possessed (and corrupted) by Masamune ultimately involved not a similar fight but a conversation.
 * In Dragonball Z, Goku and Vegeta fight projections of Piccolo, Gohan, and Gotenks in Super Buu's brain.
 * Chapter 493 of Naruto has
 * And now.
 * At one point in the Berserk manga's Millennium Falcon arc,.
 * The Manga adaptation of Breath of Fire IV has Ryu and Fou-Lu merge into Infini and then mentally duke it out for control of the creature. This is a Third Option Adaptation from the game, where Ryu either resists the merge and fights Fou-Lu's Tryant dragon with his allies, or he accepts the merge and Fou-Lu takes control of Infini, easily wipes out Ryu's friends, and proceeds to destroy the world.
 * In Weiss Kreuz Gluhen, Berger draws Crawford into his own psychic mindscape to fight him. Crawford, however, manages to turn it around on Berger and pull both of them into the center of his own mind - and unlike in Berger's, in Crawford's mind, they aren't alone.
 * Ranmaru from Tokko has to do this after an encounter with Taishi results in him losing control of his phantom.
 * Ranmaru from Tokko has to do this after an encounter with Taishi results in him losing control of his phantom.

Comic Books

 * The Incredible Hulk: During Paul Jenkins' run, one of Bruce Banner's Hulk personalities, the 'Beast', a near-mindless monster, threatens to take over completely, so Bruce journeys into his mind and recruits the three main Hulks - Savage Hulk, Joe Fixit, and the Professor - to defeat it on his/their home turf.
 * Star Wars: Legacy features a power struggle of two Sith Lords in each other minds. Lightsaber fights are blank compared to what they can achieve in that state.
 * In X-Men, obviously. For example, the only way to save a person infected by the Brood is to kill the parasite's mind ( unless you are a very good telepath you won't be able to save yourself. Heroic Resolve won't solve the matter - it is nessessary for the help to be able to arrive in time in the first place)
 * Or, you need to be Wolverine.
 * The Avengers played with this one in the 2001 annual, involving Hank Pym's separate personalities (Goliath, the cold unfeeling reason, and Yellowjacket, the impulsive showoff) who hated each other's guts getting dumped into a psychic landscape that was supposed to represent the original's mind after they were physically separated into two people in the real world. Initially, they started fighting for control, even trying to force Janet (who was back together with him at the time) to choose which one would live. Only after they both accepted the previously ignored third aspect (the human combination of both) were they put back together, keeping him from dying.
 * The final battle of Scott Pilgrim is like this.
 * The Reboot version of the Legion of Super-Heroes had a memorable one, when Saturn Girl enters Shrinking Violet's mind to help her free herself of the control of the cursed Emerald Eye of Ekron, which is using her body to attack the rest of the team.
 * PS238 had one of those when Zodon and Julie ran into a telepath. Also, minions of Order and Chaos squabble in Toby's head for a while.

Fanfiction
"Arsenal: "All you're telling me is that I've pissed in your Cheerios more than once, and I did it beside Donna. Lemme tell you, those are two things that make me a very happy little camper...And hey, extra bonus for me at the end of it? I pissed you off when I didn't even mean to! Little ol' me. A guy. A dude. A very attractive but semi-normal human fleshbag. Man, I'm good.""
 * Gekizetsu's amazing and heartfelt series 'The Month of Open Doors' begins with Supernatural's Dean Winchester locked in a room in his own mind by something. A rather strange battle in the centre of the mind plays out over the first arc, 'As Fools Shine On.'
 * The Homestuck fanfic Darkness climaxes in John, who has gone utterly insane,  On the outside, of course, he's gone into a coma.
 * Because Mind Rape was a staple of Galaxy Rangers, the Fanfic tends to break out this one quite often. Red Witch's Down the Dark Path plays it straight after Shane was tortured with the Mindnet. "Isn't Life Strange" and "Chrysalis" use it as well. Subverted in those fics as the Rangers affected lose - badly.
 * Used in the DC Nation universe after Raven's attempt to restore some of Troia's lost memories end up getting Raven, Troia, Nightwing, Flash, and Arsenal in a brawl with Dark Angel. Leads to one of Arsenal's best lines:


 * Doctor Who fanfiction The Ten Doctors features
 * In the Daria/Legion of Super Heroes Fanfic crossover Legion of Lawndale Heroes, psi-active cadets at the Military School known as the United States Academy of Extranormal Studies, or  'USAES' , can receive certification in the Astral Special Tactical Response Operations (ASTRO) course for out-of-body and psionic combat. As part of their training, cadets learn how to create a specific 'mental persona' (much like a 'Patronus') to do mental combat in and manifest their powers during that combat.
 * Taker Foxx's Imperfect Metamorphosis has so far in the story four characters sharing a same body because . It doesn't help that one of them came with a Super-Powered Evil Side. There is a Battle in the Center of the Mind between and the villain when the villain is discovered.
 * Implied in this fanvid for Tron: Legacy (spoilers out the kazoo).
 * The dwarven noble protagonist of Dragon Age: The Crown of Thorns had more than one of these, twice against actual psychic attacks by the Archdemon. The latest one had rather severe consequences for both the prince and the whole world because the Old God actually
 * Kallian Tabris also goes through something like this at one point, only.
 * My Little Pony Friendship Is Magic fanwork 'The Party Never (or Hasn't) Ended' features Twilight Sparkle having to help Pinkie Pie in one of these against Nightmare. Then Pinkie Pie helping Rainbow Dash.
 * Queen of All Oni: Throughout the story, we get glimpses inside of Jade's mind, where we watch as Hero (the Aspect representing Jade's heroic nature) gather together as many uncorrupted Aspects as he can into a La Résistance aimed at regaining control of Jade's mind from The Queen. They eventually launch an attack on the ship representing Jade's consciousness, but before Hero and The Queen can fight each other, the trope ends up being subverted—in the real world, Jade is captured by the Evil Sorcerer Lung, whose attempts to break Jade to his will end up driving her insane, which cause the mindscape to literally fall apart, forcing the Aspects to focus on their own survival.
 * Happens a couple of times in the Pony POV Series:
 * First, during Pinkie Pie's reharmonizing chapter, Angry Pie (a Split Personality representing all of Pinkie's anger) attempts to pull a Split Personality Takeover by absorbing all the other pieces of Pinkie's mind. Pinkie is only able to defeat Angry by
 * This is also the conclusion of the Trixie storyline:

Films -- Live-Action

 * In the film Dreamcatcher, based on the Stephen King novel, one of the characters is possessed by an alien being. In his mind, he locks himself in a warehouse of his memories and tries to bar the alien presence from getting inside.
 * In the psychedelic western Renegade (aka Blueberry) based on the graphic novel, the hero takes peyote and gets into a spirit battle with the villain. The forces of good are golden reptiles, while the evil side are black bugs. After defeating the villain, the hero watches a recreation of a forgotten tragedy and comes to terms with it.
 * In the Chinese film Hero Magistrate Nameless makes a show of attempting to arrest Long Sky at a Chess Court in his prefecture. They pause mid-fight, Nameless paying the resident (blind) Gu Qin master to continue playing. This he does, as they fight out the remainder of the battle in their minds. When he breaks his instrument with the sheer intensity of his playing, the fight plays out for real and Nameless defeats Sky in a matter of seconds.
 * Inception takes this trope and turns it Up to Eleven. Virtually the entire plot takes place inside a dream, battling defensive figments called 'projections' while trying to plant the Idea in the subject's mind.
 * Sherlock Holmes a Game of Shadows features an example similar to Hero:
 * In the Guy Ritchie film Revolver the protagonist Jake Green, who is claustrophobic, battles his ego when he gets trapped in an elevator. What follows is a scene that looks straight out of the last episode of Neon Genesis Evangelion

Literature
"The Guarding Dark: "Yes...but you misunderstand. I am not here to keep darkness out. I am here to keep it in.""
 * In Terry Pratchett's Thud!, when Commander Vimes is chosen as the Summoning Dark's champion, its attempts to take him over are represented as it entering a city (Vimes's mind) and being thrown out by a Watchman, representing the bit of Vimes that watches himself: the Guarding Dark.


 * This also shows up in A Hat Full of Sky, where the Nac Mac Feegle help Tiffany confront the hiver that's taken over her body by luring it into the part of her mindscape where she's most powerful, a mental representation of her home country.
 * Granny Weatherwax has a moment like this in Carpe Jugulum. (Vimes and Granny have a lot in common...)
 * Rincewind has a Hissy Fit In The Center Of The Mind in The Light Fantastic, when he berates the Great Spells of the Octavo for ruining his life, and he later subdues the Eighth Spell by figuratively hauling it out of hiding within his psyche.
 * Magician. Tomas, one of the main characters, finds a suit of cursed armor that fuses him with a godlike being, who wants to repulse the invaders (Tsuranii). Said godlike being was one of a race that created the bloody elves as their personal slaves, to the point that an elf can't disobey any word said in their language, and who are fiercely protective of their world. Now, if Tomas standing in the middle of a storm of pure mental fury from a dragonlord whilst quietly saying, "I am Tomas" isn't an incredibly badass version of this, nothing is.
 * That "godlike being" is actually a Dragon Lord, or Valheru as th elves call them. They weren't really godlike, as they all got slaughtered except one when they challenged the Lesser Gods of Midkemia during the Chaos Wars, but they're still far more powerful than any human or elf except the highest levels of magician.
 * The ally-assisted version was used in the book Prince of the Sidhe, when King Aedh of Eiru (Ireland) gets drugged by the book's villain. We see Aedh's mindscape (which is just as confused as he is), and get things from his point of view when the titular character comes to Aedh's assistance in his own unique fashion.
 * in the sixth Young Wizards book, the autistic wizard-to-be Darryl is subjected to this constantly - his "Ordeal" (a battle with the Lone Power to prove fitness as a wizard) has gone on for three months. The reason for this is that . Eventually Nita and Kit get into the kid's head to help him break the cycle.
 * George R. R. Martin's "The Glass Flower" has pretty much turned this whole concept into a story. He calls it 'the game of mind'.
 * In the Warhammer 40,000 Imperial Guard novel Cadian Blood, Seth
 * was doing a pretty good job of screwing with Harry Dresden until he realized that even is at his mercy when it's in his head. Pwnage ensued.
 * Molly fights an epic one against in Ghost Story. Apparently, the center of Molly's mind looks like the bridge of the 1960s Enterprise, complete with a crew of Mollies wearing miniskirt uniforms and mimicking the behavior of the original characters and an epic fighting music soundtrack.
 * Julia spends most of The Ragwitch trying to find a way to make some headway Fighting From the Inside the titular monster. Towards the end, this culminates in a real battle when fight for continued existence after the Ragwitch finally realizes that Julia hasn't been as helpless as she thought. A dragon and hordes of Mooks are involved.
 * Dandra and Tetkashtai get one during the climactic battle of the second book in the Dragon Below Trilogy. Though it is less of an invader vs. invaded than two splinters of one personality duking it out to see which will be dominant.
 * The Star Wars Expanded Universe Darth Bane novels use one of these to
 * Chronologically much later, in the New Jedi Order novel Reunion, Jedi Knight Tahiri gets sucked into one of these by her Enemy Within, an artificially implanted Yuuzhan Vong personality who is trying to pull a Split Personality Takeover on her. It turns out that neither of them can win, since they've become so tightly linked that destroying one would destroy the other; to save their sanity, they end up doing a Split Personality Merge instead. The whole thing is represented as a sort of really trippy lightsaber duel with injuries carrying over to both combatants.
 * In On Stranger Tides, the confrontation between sorcerers  concludes when the former attempts to re-write his own memories to bolster his own self-confidence, and therefore his power. The latter undermines his enemy's attempt to rewrite history in his own mind, crushing his opponent's psyche by exaggerating his recollection of a traumatic humiliating event.
 * The ending of Robert Sheckley's The Status Civilization is this.
 * In the Star Trek: The Next Generation Mirror Universe novel Dark Mirror by Diane Duane, Deanna's mental defences are represented by children's building blocks (when she was being taught to use her powers she heard the term "mental block" and misunderstood). Evil!Deanna batters ineffectively against these blocks, while our Deanna calmly walks into her opponent's mind as though it was her own, because unlike her counterpart, she can admit that, in a way, it is.
 * The Doctor Who Virgin New Adventures novel Timewyrm: Revelation by Paul Cornell is largely set inside the Doctor's mind, which is under attack from the Timewyrm. Different parts of the Doctor's mind are looked after by five of the six past Doctors (Sixth isn't there for reasons we learn later), and there's an area where the six "embryonic" personalities of Doctors-to-come wait to be born.
 * In Sergei Lukyanenko's Night Watch series, the battle for dominance between Vampires apparently works like this. To an outsider, however, it looks like a glorified staring contest.

Live-Action TV

 * Farscape made this into an art form with John's confrontations with Harvey-Scorpius. This resulted in one of the best episodes anywhere ever: a Looney Tunes style cartoon showdown, including all the old favourites (painting a wormhole on a wall only for someone to drive through it...).
 * In the Doctor Who serial The Deadly Assassin, the Doctor and the Master tap into The Matrix (a psychic computation matrix) and have a battle of the wills—the landscape in the Matrix is created by their brainwaves, so the Master can basically create an entire world through his will and makes the Doctor suffer various tortures in it, nearly killing him.
 * In The Three Doctors, the Third Doctor and Omega have a mental battle in which Omega is represented by a goblin-like creature.
 * Highlander the Series' Duncan MacLeod has two of these:
 * The first one while under the effects of a "Dark Quickening", between his noble self and the evil he has absorbed through centuries of beheading evil immortals.
 * The second one against the demon Ahriman.
 * The Red Dwarf episode "Gunmen of the Apocalypse" has the main characters enter Kryten's subconscious to help him fight off a computer virus.
 * Angel vs Angelus, with Faith present as well.
 * During Power Rangers Dino Thunder, Tommy spent several episodes stuck his Ranger suit, then unable to turn his invisibility power off so that his actor could visit his family. His first episode back involved him becoming visible again, but putting himself into a coma in the process. He then had to fight his previous Ranger identities. After barely getting past Zeo Ranger 5 and the White Ranger, he had his ass thoroughly kicked by the Green Ranger, but still refused to quit - at which point they allowed him to wake up and restored his Dino Gem into the bargain.
 * Happened a couple of times in Stargate Atlantis, memorable examples being Dr. Weir facing off with Oberon in her mind to allow her teammates to escape the other Replicators, Teyla fighting off the Wraith queen's attempts to probe her mind, and Sheppard fighting himself (sort of) in his own mind.
 * During the Supernatural season six finale,
 * In The United States of Tara,

Machinima
"Sarge: Arrr, I be havin' a southern accent. Arrr!"
 * Red vs. Blue (more specifically, Church and Tex) took a trip into Caboose's mind while he was semi-possessed. Interestingly, the actual fight against the evil force is done against a backdrop of the actual Red Vs Blue war ... with a few unique ideas of who's involved.

Music
"I'd need a shotgun in my dreams tonight To terminate my rotten side."
 * "The Trial", the climax of Pinky Floyd's 1979 Rock Opera The Wall, features the main character put on trial in his own mind and convicted by a monstrous imaginary judge.
 * Kitananx made a song CALLED Battle In The Center Of The Mind.
 * "Heaven Tells No Lies" by Helloween invokes this in the chorus:

Tabletop RPG

 * Dungeons & Dragons
 * Illusion spells 'Phantasmal Killer' and 'Weird' work a lot like this trope, in that they create a personalized Imaginary Enemy that get killed the targets who fail to resist their terrors.
 * In Ravenloft, recurring nightmares occasionally attract the attentions of a group of darklords called the Nightmare Court, who, as their name suggests, try to play it up until they reduce the ailing victim into a comatose wreck. Needless to say, any adventure involving them is about kicking their ennui out of the head of the dreamer while sorting out his issues.
 * Dark Sun Sourcebook The Will and The Way introduced "harbingers" and "constructs"—mental forms that tweak and help to focus telepathic combat powers. The question whether both sides see the same is avoided, but on Athas psionics is well-codified, thus everyone learns the same set. So you end up with mental attacks and defences put into images such as a giant scorpion trying to undermine a wall or flames trying to burn through a beetle's carapace.
 * A possible occurrence in the "Zorandar" setting from Hero Games' "Lands of Mystery". If you get captured by one set of enemies, they'll try questioning you telepathically. Resist, and the telepathic struggle is gamed out as a one-on-one fight between your interrogator and you. If you lose the fight, the interrogator gets the answer to whatever question set this in motion. If you win, you wake out of the mind trance to find your interrogator has just suffered a brainfry (and if you can't figure out that this is the perfect time to escape ....)

Theme Parks

 * This is the entire premise of the Fantasmic show at Disney Theme Parks, with several Characters invading the imagination of Mickey Mouse.

Video Games

 * Raz in Psychonauts fights (and helps defeat) the Freudian Excuses lurking in people's brains—such as a painter's anger (which manifests as a bull), a former insane asylum warden's split personality (which looks like Napoleon and against whom he is constantly trapped in a war game), and
 * In Drakengard 2, Nowe fights one of the boss battles in Manah's mind after she has her Heroic Villain Protagonist BSOD.
 * If you decide to attack the Mindflayer Elder Brain in Neverwinter Nights: Hordes of the Underdark, it will suddenly trap you inside an illusion where you are waking up from a dream. If you accept it, you get a non-standard game over. If you reject it, you will be attacked by monsters within the dream and upon defeating them you will return to reality and the Elder Brain will beg for mercy, allowing you to make a deal with it or deal the killing blow.
 * In Splatterhouse 3, Rick fights the final boss,, in an Amazing Technicolor Battlefield that represents his psyche.
 * According to Word of God, Cloud's one-on-one final battle with Sephiroth in Final Fantasy VII is this.
 * In Kingdom Hearts: Chain of Memories, when Riku fights off Ansem.
 * And there's another one in Kingdom Hearts II,.
 * Special mention to that.
 * Happens yet again in Kingdom Hearts: Birth By Sleep with and   with   pitching in during the True Final Boss fight.
 * The purpose of Alice's nightmarish return trip through Wonderland is this.
 * The Incredible Hulk: Ultimate Destruction has a boss battle in Bruce Banner's subconscious, where the Hulk takes on Banner's underlying hostility and malevolence, officially dubbed "Devil Hulk".
 * Sort of happens in EarthBound, as Ness has to fight his own Nightmare at the end of his dream world known as Magicant. (Averted in Mother as that Magicant is dream instead of Ninten's. A fight with Lucas's Nightmare was removed from Mother 3, which has no Magicant.)
 * Happens near the end of Planescape: Torment when you have to enter a mindtrap and
 * Late in Jeanne D'Arc,, Gilles, and Richard are whisked into an abstract representation of 's heart, bound by chains by the Reaper Ira. The three of them must battle Ira's cronies to destroy his power over ; eventually, a manifestation of 's spirit joins the three heroes to assist them, particularly because is what caused  to submit to the Reaper.
 * In Final Fantasy VI, sleeping at Doma Castle with Cyan along will cause the party to be taken into Cyan's mind, where they can battle a demon called Wrexsoul that is feeding off his survivor's guilt for when his kingdom was wiped out.
 * Also, the final battle of Final Fantasy VII.
 * In Shin Megami Tensei I, you find a young girl whose mind has been infested by a demon that is devouring her from the inside-out. You have to dive into her mind in order to kill the demon and save her.
 * Tales of Symphonia: Dawn of the New World: If you go for the good ending, this is the final battle. Given how different Emil's and Ratatosk's personalities were, though, the player was probably expecting something like this to happen (although it's a lot less confrontational than you might expect—whichever way the fight turns out, the two accept each other).
 * The battle against  in Prince of Persia The Two Thrones turns out this way. After some platforming, you end up with him and yo, the solution being.
 * Happens no less than three times in Jade Empire:
 * Two demons vie for control of a little girl's body. You have to pick which one you'll support, and then it's a kung fu battle inside her mind.
 * Near the end of the game, you can attempt to wrest control of The Dragon away from the Big Bad. You control the ghost of the Dragon's past self and fight its current incarnation.
 * When you confront the Big Bad himself, he attempts to overwhelm you with despair. Naturally, this means you have to fight some freaky glowing swordsmen named "Despair" in an Amazing Technicolor Battlefield. You also get to rely on the Power of Friendship for encouragement, which takes the form of your allies running up to the "Despairs" and, um, exploding.
 * The Kalecgos encounter in World of Warcraft: Burning Crusade. The players are supposed to free the good dragon from a dreadlord that is mind controlling him.
 * An odd example where you're the invader is in the fight with the Cosmic Horror of dubious quality, Yogg-Saron. During the fight with him, portals into his mind open up, where you then have to desperse the memory of an important event in Warcraft lore so you can get at his brain. Of course, he knows you're in there, so he then attempts to whittle down your sanity so that he can Mind Control you, so you have to soon get out so that you can take a rest in one of the Sanity Pools.
 * Every boss fight in Persona 4 is this until close to the end of the game. Although it's more like "Battle In The Center Of The Collective Unconcious".
 * Not quite the same, but not quite anything else either: In Maken X, Kei's consciousness (using Kei's form) spends most of the game standing on a glassy-looking disc in her brain yelling/screeching at her body, now possessed by the Maken.
 * Near the end of Sam and Max Freelance Police "Culture Shock", Sam falls under the hypnotic sway of disgruntled former child star Brady Culture. After snapping himself out of it by a blow to the head from the security system at Bosco's Inconvenience Store, Sam finds himself in his own mind. There, he has to dispose of a host of Brady Culture clones that represent Culture's hypnotic influence.
 * The finale of Arcueid's and Archtype Earth's plots in the "Current Code" version of Melty Blood is this between them.
 * Battle Moon Wars has this in Tohno Shiki's mind while he lies unconscious, fighting internally against Nanaya Shiki. Unfortunately for him, he also visualizes Akiha and Satsuki in this mindscape and thus is unwilling to fight at first. Insert friendly telepath encouragement as Sion uses Etherlite to join in and help him out.
 * The final battle in Dead Space 2, where Isaac fights
 * A rather weird one in No More Heroes 2 Desperate Struggle where Henry, while unconscious, fights against Mimmy, a manifestation of Travis' various fetishes (being a Moe Robot Girl), which is apparently brought on by Travis "watching" anime in the other room.
 * Anyone in the Penumbra series who gets infected by the Tuurngait gets one of these, although you only play through Philip's. He and Red both win their battles, retaining a measure of self-control (and, in Philip's case, splitting off his own infestation from the Hive Mind to make it an easier-to-manage Enemy Within.) Everyone else who appears in the series lost and got assimilated.
 * The sixth arc of Umineko no Naku Koro ni involves a duel between that is a thinly-veiled version of this, with  sitting on the sidelines. The seventh arc reveals that this has been the state of affairs within  head for a good year or two prior to 1986. Once  is forced off the sidelines by Battler's return, the entire duel is scuttled, however.
 * Happens twice Batman: Arkham Asylum when Batman gets drugged by The Scarecrow, resulting in massive Interface Screw and a Fission Mailed before entering a twisted world based on his psyche. However Batman manages to fight it off due to Heroic Willpower, to the horror of Scarecrow. It also happens in the sequel with.
 * In The Elder Scrolls V: Skyrim, Sheogorath takes you to his personal vacation spot: the mind of Pelagius the Mad and will only agree to leave if you humor him and combat Pelagius' various psychoses with the help of his artifact, the Wabbajack.
 * The climax of Metro 2033
 * The Very Definitely Final Dungeon of Neverwinter Nights 2: Mask of the Betrayer.
 * The Very Definitely Final Dungeon of Neverwinter Nights 2: Mask of the Betrayer.

Web Comics
"Nanite: Look, we told you already... that thing won't work in here. It's just a metaphor." Schlock: But a meta for what? I have a pretty good immune system..."
 * Liquid's battle against the Ghost of Big Boss for control of his body, in The Last Days of Foxhound.
 * Dominic Deegan, several times. The titular character's main strength is his mental abilities. And it's established that on the psycho planes, a being's physical size is directly proportion to how powerful their minds are.
 * Shows up in Schlock Mercenary when everyone's favourite carbosilicate amorph is infected with nanite AI that hacks into his brain. When Schlock pulls out his plasma cannon, the nanites are initially unimpressed:

"MaKo: If you're not a product of my subconscious, you're about to have a very bad night."
 * Later, when two brain hijacks ran into each other:


 * A variation occurs in Charby the Vampirate when Tony has to use his Alp powers to enter Zeno's mind and help him fight the spirit possessing him. Turns out that Zeno has pretty much given up the fight already and is of no help, so Tony changes tactics and get the spirit to not only force him out but to enter his mind instead. A big mistake, as it gave Tony a massive homefield advantage.
 * Torg from Sluggy Freelance faces one of these during the "Wayang Kulit" Story Arc. In this case he's fighting all of his major past and current Love Interests. Bit of a subversion, in that killing them only makes things go worse for him.
 * K in Blip, when she was in rage. First she kicked out her friends, then for lack of semi-real targets imagined and destroyed a Pirate Transvestite Robot.
 * The Order of the Stick: Haley’s “mental constructs” have a habit of bickering amongst themselves, at least until she makes them all sit down and shut up.
 * Happens between Artie and Joel in Concession, but ultimately spills over into the real world. Doubles as a subverted "I Know You're in There Somewhere" Fight as unfortunately, that part only works for a little bit.
 * Monique from Sinfest once tried to defeat a rhinovirus with(in) her mind.
 * Critical Miss explains the principle.
 * Eerie Cuties has this going in chapters 17 and 18.

Western Animation

 * Superman going inside Brainiac 5's mind in the second Season Finale of Legion of Super Heroes stirs him to fight the brainwashing. There was also a Fusion Dance involved.
 * Princess Tekla from Shadow Raiders, who fought Lamprey when the latter took over her body.
 * The Teen Titans episode "Nevermore" takes place in Raven's head. Needless to say, it is a scary place.
 * The Spectacular Spider-Man faced down this way.
 * The 90s X-Men cartoon was fond of this, and would make elaborate battles in a mindscape shaped by the combatants, making the grandest, most awesome (and trippy) affairs out of scenes that were basically two people glaring at each other in the comics. The most notable instances would be Professor Xavier versus the Shadow King, Jean Grey and Rogue versus Ms. Marvel's transplanted personality, and Professor Xavier going toe-to-toe with Dark Phoenix in Jean's mind (a duel only shown through a series of effects-laden panels in the comics).
 * In an episode of the 90s' The Incredible Hulk cartoon, Banner was possessed by a demon; Green Hulk and Grey Hulk joined forces to kick him out of their shared body. Several episodes also showed the two Hulks fighting for control when Banner hulked out.
 * The symbiote asserts its dominance this way during its introduction in Spider-Man: The Animated Series, manifested as the symbiote and a giant Spider-Man costume struggling over Peter Parker. As surreal as it was, it was arguably one of the series' better fight scenes...
 * The last episode of the Disney's Aladdin cartoon to have Mozenrath in it ended with Mozenrath attempting to possess Aladdin's body after his own suffers total organ failure from overuse of dark magic (which turns out to apparently be the source of his interest in Aladdin through most of the series). After he stops being afraid, Aladdin uses the Power Of Love to curbstomp Mozenrath's ass. This would have been a fitting end for the series Big Bad, but being a Disney cartoon he gets better at the end to menace Agrabah another day.
 * In Fairly Oddparents, Timmy and imaginary friend brought to life Gary battle in Timmy's mind.
 * In Young Justice Miss Martian and Psimon have a psychic battle of this sort. M'gann is invisible and Psimon is still psychically protected, making it difficult for the fight to be cut short mundanely.
 * The last episode of Mighty Orbots has the heroes physically entering the body of their archenemy, the titantic supercomputer Umbra. This results in them finding themselves in his mindscape and having to fight off manifestations of his evil thoughts.