Psychoactive Powers

"Hiroim: Impossible... Caiera: He shifted the very plates... Korg: Of course he did, he's the Hulk. Caiera: But you said he couldn't. Korg: I was just making him mad. He seems to work best that way."

- Planet Hulk

Our hero has acquired a new onboard superpower through the power of an origin story or receiving Applied Phlebotinum. Unfortunately, the effectiveness of the power or device depends on the mental stability and/or confidence of the user. Inherent to The Dark Side.

Naturally, tends to be an example of Personality Powers. Not to be confused with Psychic Powers or powers from psychoactives. Compare Heroic Spirit, which may overlap with this trope.

Anime

 * Tengen Toppa Gurren Lagann. The mecha of the series, called Gunmen, are powered by Spiral Energy, which comes from living things. The amount of Spiral Energy one produces is tied directly to their emotional state. Fear and despair lower it, hope and optimism increase it, and Hot Blood blasts it to Over Nine Thousand.
 * Haruhi Suzumiya fits here. Subverted of course, since Haruhi doesn't know.
 * Also, it depends on mental instability, and the rest of the cast spends a great deal of effort preventing this.
 * Neon Genesis Evangelion
 * Specifically, synchronisation strongly depends on the part of the brain associated with certain emotions, such as those between two lovers, or the love of a parent and child, hence all the SoulJars and Mommy Issues orchestrated by NERV
 * The Lambda Drivers that power the Humongous Mecha in Full Metal Panic! work like this. The Techno Babble basically stated that it runs on Applied Phlebotinum that begins generating energy when exposed to brain waves above a certain level, which are reached when the brain is processing especially intense emotion.
 * The bad guys found a way around this, by using a drug to keep their Lambda operators at peak emotion at all times. Has some side effects.
 * Orihime's abilities in Bleach are restricted by her willpower. Her powers could be very powerful offensively  if she actually wanted to hurt anyone, but she's an Actual Pacifist, and so generally only uses them for healing or defense.
 * The N.O. portal connecting Medica Mechanica to Naota's head seems to get wider during times of emotional distress.
 * In Yu Yu Hakusho, Kuwabara is undoubtably the weakest of the heroes, but has proven capable of short bursts of incredible power when properly motivated/inspired.
 * Soul wavelengths in Soul Eater. Mindset affects both the powerful moves that require a high level of soul resonance between meister and Weapon, and the basic ability of the two to work together.
 * Goku of Dragon Ball. When the chips are down, he'll take a beating and be on the ground battered and bruised—but The Power of Love is Goku's secret weapon. Remind him his loved ones will suffer if he doesn't get back up, and he'll find hidden reserves of strength and deliver a curb stomp to the bad guys.
 * It's true of his son Gohan even from childhood. As a small boy, his power level is a 1 when he's scared but when he's angry it climbs and keeps climbing, enough to nearly knock a full blood Saiyan off his feet.
 * The I-field barriers used by the SUMOs in Turn a Gundam are said to operate at least partially on the pilot's willpower (which goes a long way to explaining why Harry Ord's is so strong). The Moonlight Butterfly will also only manifest when the pilot has the proper amount of determination to activate it.
 * The Gundam Unicorn's NT-D system only activates when the pilot is under a certain amount of emotional stress ... typically anger or fear (common battlefield emotions), but Banagher manages to activate it in episode 4 through determination to help someone.
 * Dragon Slayer powers work this way in Fairy Tail. Happy actually revs Natsu up into beating a Big Bad by suggesting he should back off and let Gray handle it.
 * Chaos;Head has the Di-Swords, only functional through... delusions. Thus, in somewhat of a departure from the classics, the user has to be screwed up in order to use the weapons. This, though, is only fitting in a show such as Chaos;Head.

Comic Books

 * Empowered: Emp's theory about her suit being shredded easily because her self confidence and self esteem are easly shredded is entirely accurate. When she's not thinking about ending up in Damsel in Distress territory, she can make really effective use of the suit. On top of that, when  because the motivation there was to make Emp look like a force to be contended with. Also,   so doesn't suffer the confidence problems Emp does.
 * Of course the thing does not grant powers to anyone aside from Ms. Powers either....
 * The Green Lantern Ring - if the user doesn't have a strong will, getting the thing to so much as light up is a herculean task. If the user has a decent will, they'll be able to create constructs, but they won't hold up well in battle when the user is frightened or rattled. If the user doesn't have much of an imagination, it forms very boring and mundane things.
 * And now there's a whole spectrum of colors that require feeling or inspiring a specific emotion (rage, greed, fear, will, hope, compassion, love) in order to work.
 * As of the recent Captain Britain and MI: 13 series, Captain Britain's powers work like this; super strength and durability in proportion to his confidence and emotional stability.
 * Gladiator, AKA Kallark, of the Marvel Universe, is like this; his power is based on his confidence. This spirals both ways; being the most powerful mortal in the universe when he's on top of his game, he's ever-more-confident when things are going his way- but when something finally does go wrong for him, the shock can make his power collapse quick.
 * Spider-Man's powers have stopped working several times due to emotional issues, in almost every medium that he's been in. He gets them back when he becomes self assured again, usually just in the nick of time.
 * The Incredible Hulk. Bruce Banner only turns into the Hulk when angry, and then the angrier Hulk gets, the stronger Hulk gets.
 * This does depend on the writer; sometimes the Hulk's transformations are portrayed as the result of adrenaline, both in the form of anger and excitement or fear, other times it is portrayed as a pure survival mechanism, activating to save Banner's life regardless of emotional state. But the anger fueling strength connection is generally maintained.
 * She Hulk (Jen Walters, that is) can usually use her powers at will, but she has been stuck before in her Hulk form due to subconscious unwillingness to change back, and in her human form when she was too scared to become She Hulk again. If you make her angry enough, she can also turn into a Savage She Hulk that is very reminiscent of he cousin's form.
 * Superman once lost his powers for a year, then got them back when he cheered up and enjoyed his life.
 * In Marvel the superhero Speedball, after becoming Penance, found that his new powers only worked when he was in pain. Cue the iron maiden styled combat suit. It was also implied that he could once again use his old powers if he overcame his depression, and that they relied on him being happy. As the Fun Personified character he had been before Civil War, it makes some sense that this had previously not been noticed.

Film

 * Will Stronghold of Sky High is an arguable example. Will was in the gawky, awkward stage of adolescence, and had no confidence. He also had no powers, but hadn't made the connection between the two. The fear and shame involved in the idea of disappointing his superhero parents also didn't help. But when Warren put his friends in danger, Will grew confident and his powers suddenly manifested in the middle of the fight.
 * The male lead in My Demon Lover only transformed into his formidable demonic aspect when he was horny enough.
 * In In the Name of The King: A Dungeon Siege Tale, the Big Bad Gallean goes mad with power and gains abilities not normally available to the magi. During his magical duel with Merick, this is the only thing that allows him to surprise and defeat the more experienced magus.

Literature

 * One of the stories in the Azazel series by Isaac Asimov involves an irritating atheist given a Jet Pack and told that it's powered by his belief in science and logic. The problem is,
 * Skeeve in Another Fine Myth must stop drawing upon his parents' or mentor's strengths for his confidence, and find it in himself instead, to finally light a candle with his magic.
 * Wild Cards: The school of thought that Aces are internally confident and end up being beautiful and powerful, while Jokers have some sort of internal self-hatred that manifests outwardly. This also reflects in their powers, because some Jokers have powers that would make them Aces if they weren't so hideously deformed.
 * The wizards in Discworld are like this.
 * Nynaeve in The Wheel of Time can only use her magic when she's angry.
 * In The Dresden Files, Harry's magic is partially based on emotion. On several occasions, he has gotten very angry and used it to amplify his fire magic. On another occasion, he has used a surge of lust induced by a White Court vampire to power a shield spell.
 * He has also stated that sometimes color can become part of the spell, as seen in Proven Guilty when he builds the net to find the phobophages. There's black for vengeance, white for purity, etc. When building the net, he uses blue play-dough because of blue's connotations with defense. Plus, blue is cheaper.
 * In Larry Niven's Known Space universe, this is how Gil "The Arm" Hamilton got his power and nickname. He had lost his right arm in an accident, but one day when he absent-mindedly tried to catch a dropped object with the missing arm, he manifested an "imaginary" psychic arm that works via telekinesis. One story notes that psychic abilities work only because the user believes in them.
 * It should be mentioned that while Gil's arm can handle hazardous materials and reach through solid objects or live video feeds, it is otherwise limited to the same range as his flesh-and-blood arm (arm's reach), and only strong enough to lift a pound or two in Earth's gravity. People have asked Gil why he doesn't try hypnotherapy to correct these shortcomings; he points out that feeling like he has an arm ten feet long might interfere with his Willing Suspension of Disbelief and make his arm go away entirely.

Video Games

 * The central gameplay mechanic of Super Princess Peach is activating one of four "Vibes", which are abilities based on four emotions. In Joy, she gets the ability to float. In Rage, she gets surrounded by fire and gets a Shockwave Stomp. In Gloom, she gets Ocular Gushers that spray Swiss Army Tears. In Calm, she heals herself.

Web Comics

 * Zimmy from Gunnerkrigg Court has some kind of Psychic Power (her exact abilities are rather vague so far). She also has a mental disorder—she describes it like having static in her head. The worse the static gets, the less control she has to prevent her powers from acting up.
 * El Goonish Shive: has Telekinesis just strong enough to "arm-wrestle". But when someone makes her explode (figuratively), something may explode (literally).

Western Animation

 * Presto from Dungeons and Dragons had this problem. No confidence in his abilities, so his magic worked sporadically, and rarely as intended.
 * In one episode of Danny Phantom, he temporarily gains the ability to control the weather, but it's based on his emotions instead of consciously controlled.
 * This also applies to his general ghost powers during the beginning when it was more sensitive to his growing emotions.
 * In Teen Titans, Toonverse Starfire's powers are apparently triggered and/or powered by specific emotions, eg joy for flight, rage for Eye Beams etc. Naturally this little factoid first cropped up when she got bodyswapped with Raven, whose powers go haywire without tight emotional control. It comes up again later, when Starfire finds herself unable to fly because she's confused as to the status of her relationship with Robin.
 * Rex's powers from Generator Rex require him to be focused and level headed when using them. If he loses his concentration, for instance if he becomes confused his powers will fail.
 * Bending works this way in Avatar: The Last Airbender. Aang has to adjust his mindset when he learns a new element, which becomes a serious problem with the happy-go-lucky hero has to learn to be steadfast and forceful to learn Earthbending. Zuko also loses most of the power behind his Firebending when

Live Action TV

 * Chuck's Intersect 2.0 flashes only when he is calm enough.