Backup From Otherworld

Wherein somebody no longer of this world (often a dead friend or relative) assists a living character, directly. This doesn't refer to mere advice or moral support; this is when the dead character actually has a physical (usually magical) effect on the world of the living. This can include Spirit Advisor, offense, defense, and often healing. See also Dead Ex Machina.

If the backup comes all the way back, it may be a Battle Royale With Cheese.

Compare Army of the Dead, where this trope is applied to an entire fighting force.

Anime and Manga

 * Goku at the end of Dragonball Z's Cell Saga is the Trope Namer, when he assists Gohan in delivering a superpowered Kamehameha Wave.
 * A couple even more direct examples occur in the Buu Saga, where first Goku (still dead from the aforementioned example) helps take on the various villains of the arc before he has to return to the Afterlife, and then later, when the previously-deceased Vegeta is allowed to return to Earth to help fight Buu after his Heroic Sacrifice didn't finish the monster off.
 * In Bojack Unbound, Goku teleports himself out of the Otherworld for an instant and punches Bojack in the face to save Gohan.
 * Cardcaptor Sakura: Sakura's mom, Nadeshiko, catches Sakura after an illusion (of Nadeshiko, go figure,) tricks her into walking off a cliff. Nadeshiko reappears at the end of the episode long enough to see Sakura off to school before vanishing again.
 * In Mahou Sensei Negima, Jack Rakan forces himself back into existing by sheer willpower, and snaps Negi out of his Super Powered Evil Side. With his fist.
 * Aerith at the end of Advent Children.
 * Appleseed (2004). While Deunan is trying to deactivate the attacking robots at the end of the movie, her dead mother finishes entering the abort code for her and saves the day.
 * Subverted in Higurashi no Naku Koro Ni. In Minagoroshi-hen, Rika's True Companions come back to help her right when the Big Bad is about to ritualistically kill her... with moral support. She does die, but she gets better.
 * Mermaid Melody Pichi Pichi Pitch has Sara who comes back as a glowing spirit to save Luchia's little pink behind.
 * In Yu Yu Hakusho, when Kuwabara needed to study for an exam while Yusuke was dead, Yusuke went into his dreams and helped him study.
 * He also possessed a girl for a few minutes to beat on some bullies and a few other minor things before being brought back. This is the anime version; I hear that arc of the manga is significantly longer.
 * How Mato found Yomi when she went to the Otherworld in Black Rock Shooter; through the help of the eponymous being; if one goes by the "BRS is a spirit" interpretation.
 * In the climax of Zeta Gundam, Kamille uses his Psychic Powers (with a boost from the Zeta's Biosensor) to call for help from the spirits of his slain friends and allies, which shuts down Scirocco's Humongous Mecha and allows Kamille to ram it.

Comic Books

 * In DC Comic's Infinite Crisis while The Flash (Bart Allen iteration) is battling Superboy prime a rift in the speed force opens up and from it emerge Max Mercury, Johnny Quick and Barry Allen to help him pull Superboy Prime in.

film
"Valeria: Do you want to live forever?"
 * Ghost (1990). Sam Wheat was murdered and became a ghost. At the end of the movie he saves his girlfriend from being killed by his murderer by accidentally causing the Villain's death.
 * The Lord of the Rings: The Return of the King had the heroes recruit help from an army of the dead.
 * Conan the Barbarian: Valeria appears just in time to save Conan from being killed by Rexor, Thulsa Doom's lieutenant.


 * In Robert E Howard's "Queen of the Black Coast," this role (and indeed most of Valeria's roles) was fulfilled by Belit, the title character of the story.
 * In the remake of House On Haunted Hill, the last two characters are trying to escape from the evil presence, but there is a gate which they can't open. Before they are consumed, a ghost from a character that had entered the house with them under the same pretenses but had died earlier appears and opens the gate for them.

Literature

 * Necromancers in Kelley Armstrong's Women of the Otherworld series often get assistance from the dead, usually in the form of advice or spying, although in one book a poltergeist (telekinetic ghost) provided some more direct assistance.
 * In Splinter of the Minds Eye, the very first novel of the Star Wars Expanded Universe, it's not actually stated that Obi-Wan Kenobi briefly possessed Luke Skywalker in order to fight off Darth Vader, but considering the sudden dramatic uptick in Luke's dueling skills and the fact that he told the Sith "I am Obi-Wan", this is generally what fans assume happened.
 * In Book Three of The Dresden Files, Harry is being hunted by a ghost who vastly overpowers him. So what does he do? He fakes death, gets resuscitated, and then team up with his own ghost to open a can of whup-ass on his foes.
 * He doesn't just fake death; he actually DIES. But he has someone recuscitate him so he can then do the previously mentioned team-up.
 * In Book 13, he is the backup.
 * In the first Green Rider book, Karigan gets possessed by the ghost of F'ryan Cobblebay (Green Rider and swordmaster in training) while fighting the renegade Weapon Torne. Between the sudden change in skill level and the anti-theft spell on the brooch Torne had stolen from Karigan, F'ryan was able to defeat Torne.
 * The Lord of the Rings: The Return of the King had the heroes recruit help from an army of the dead--let's not forget it was literature before it was film.

Live Action TV

 * Randall And Hopkirk Deceased: The late Marty Hopkirk comes back to help his detective partner Jeff Randall, who's the only person who can see him except for the odd psychic or drunk. This help includes some limited ability to manipulate objects.
 * Veronica Mars season one: the late Lilly Kane is a major motivator in the solving of her own murder. Her ghost appears to Veronica and to her brother Duncan, metaphorically. Or is it? She shows up in season two to save V's life.
 * Possibly the end of season two of 'being human' where Annie takes the evil priest through the door.
 * John Winchester appears at the end of Supernatural's second season, having escaped through a hellmouth and proceeds to supremely own Azazel.
 * Actually, he only manages to struggle with Azazel for for a few moments before he breaks free, but that still gives Dean the chance to grab the Colt and use it to finish Azazel off.
 * In Kamen Rider OOO,

Video Games

 * The deceased Lirum in Lost Odyssey revives her children Cooke and Mack after a crippling defeat at the hands of Big Bad Gongora so they can in turn heal the rest of your party.
 * Alma from First Encounter Assault Recon, in a twisted way. In the non-canon expansion pack Extraction Point, she often wipes out incoming Replica troops and opens paths for the Point Man, for a good reason. Even better: FEAR 2, the reason being she's in love with the main character, Becket.
 * Only by the loosest definitions of the word.
 * After her death in Ace Attorney, Mia Fey's job is mostly to lend moral support and helpful advice. However, when  she shuttles between possessing Pearl and Maya in order to carry messages between the two parties.
 * The entire point of Ghost Trick. Sissel  is the supernatural backup for his human allies.
 * The Final Boss Fight of Final Fantasy IV hinges on this trope, with all the ex-party members aiding the party after the Big Bad defeated them.
 * Technically, only Tellah was actually dead.
 * of Final Fantasy X does this.
 * Kane in the original Shining Force game, summoning a lightning strike to stop the Big Bad from possessing the main character.
 * In the final battle of Persona 3, Shinjiro Aragaki chips in with some healing, giving the Player Character the last bit of HP needed to win the fight.
 * In the final battle of the A path in Valkyrie Profile Covenant of the Plume, shows up to lend a hand.
 * Star Fox 64: James McCloud, complete with apparent ghostly spaceship, appears at the end to guide his son out of Andross's Taking You With Me attempt.

Webcomics
"Soon: Ghost-martyrs of the Sapphire Guard, ATTACK!"
 * The ghost of Squeeky-Bobo from Sluggy Freelance helps out the Dimension of Pain demons now and then.
 * Order of the Stick: The truth is, those paladins guarding Soon's gate weren't there to guard the gate alone... they were there as reinforcements.

Western Animation

 * Prowl pulling Optimus Prime out of the Allspark field in Transformers Animated.
 * In Transformers Cybertron,
 * And a season before that, Superion's fallen brother appears to briefly help him in the final battle with Bruticus Maximus.
 * In Thunder Cats, an ancient spirit is menacing the team. It can hurt them (because of its Thundarium Mace), but they can't touch it. The Sword of Omens summons Jaga, the deceased mentor, to wield it in a ghostly battle in the sky.
 * Avatar: The Last Airbender: Dead Avatars often come to the current Avatar's aid. Sure, to do that, it means possesing his/her body in an Unstoppable Rage, but it does help. (Usually).

The season 1 finale also involved Aang getting some direct help from the Ocean Spirit itself when the Fire Nation finds a way to "neutralize" the Moon (and thus all waterbending). Both the Ocean and the Moon spirits crossed over to the physical world ages ago in Avatar, but they were still otherworldly in nature so it counts.