Power causing insanity in fan works.
Crossovers
- Child of the Storm:
- Gravemoss gets hold of the Darkhold and goes completely nuts. However, it is quite clear that he was pretty mad to begin with, so it doesn't make all that much difference to his sanity. To his capabilities, however...
- The power of the Phoenix is insanely volatile by nature, which is why She needs to act through Hosts in the first place — their conscience and rationality acts as a Restraining Bolt. However, her power tends to have a corrosive effect on the sanity of those who aren't totally emotionally balanced and in control; the power of the Phoenix magnifies emotions and is magnified by strong emotion in turn. In other words, you've got a vicious circle where the start is an insane Reality Warper who can make the Laws of Nature sit down and shut up, one who gets even more powerful the madder they get, and the end is a nigh-omnipotent Humanoid Abomination who wants to burn everything. For context, the last time a Host went mad and became the Dark Phoenix (Surtur), they wiped out a galaxy. Needless to say, there's a good reason why a) the Phoenix is so incredibly picky with Her hosts, b) doesn't usually stick around, c) is universally regarded by gods and demons alike as The Dreaded. However, as noted above, the insanity part isn't an inevitable result. It's pointed out that a sufficiently sane host — not one who suppresses their emotions, someone who accepts them, but isn't controlled by them — is perfectly capable of controlling the power of the Phoenix. But if they slip...
- The Equestrian Wind Mage:
- It's explained that the reason Vaati become an outright villain (rather than selfish and neutral) is because the surge of power from when he was first released from the Four Sword went to his head. He's worked hard at getting back to normal.
- When Grey Hoof allies with Ganondorf, the latter grants him a power up in the form of changing him into an alicorn called Nightmare Grave, which renders him even more unstable than he already was.
- The Infinite Loops is about a bunch of fictional characters reliving their stories over and over again. They gain incredible powers and also incredible neuroses. In fact, this trope is referenced by name.
- The Night Unfurls: Shamuhaza is an Evil Sorceror who attempts to harness the power of the Eldritch Truth, and later turns into an Eldritch Abomination himself, throwing away his rational thought entirely. Of course this happens. Compare him with his foil, Kyril Sutherland — a far more powerful Eldritch Abomination in human form, yet with tons more experience and restraint.
- Spark of Creation
: Kaguya Otsutsuki is shown to have been driven insane from eating the fruit of the Shinju as she spent the rest of her life with her mind connected to that of a Blind Eternity.
Animorphs
- Animorphs Redux: Used for David, the former sixth Animorph, who receives enhanced morphing powers from Crayak that allow him to literally absorb other beings when acquiring them (including Cassie), but at the cost of all the new memories he's absorbing in the process driving him insane.
The Dragon Prince
- The White Mage: Zigzagged with archmages. It's stated over and over that, while some archmages managed to keep their heads and went on to become revered figures in history, most are unable to handle the massive amount of power and go mad with it; played straight with Aaravos himself, who was one of the ones who fell to the corruption. Seemingly defied with Callum, who has become a bit short tempered with his raise in power, but doesn’t appear to be near going insane with it.
My Little Pony
- The Changeling of the Guard: It turns out there's a very good reason why most Changelings don't try to shapeshift into Alicorns... this trope and total burnout are the results, as Idol learns the hard way.
- Fallout: Equestria: The Goddess, as if the self-given name wasn't a dead giveaway. She is an immensely powerful gestalt psyche that commands the alicorns of the Unity. Unfortunately, being a disharmonious merging of some of the early-war era's most powerful unicorns (including Twilight Sparkle and Trixie, the latter being the first victim and the most dominant persona) means that she's not at all mentally healthy. In Project Horizons, we find that the Goddess likes to take every bad memory, every indication of a shortcoming or flaw, and shunt them into the head of Lacunae, an exiled alicorn whose position at Hoofington means she's not fully connected to the Unity and can be tuned out, which means that the Goddess won't grow and improve in any way, although Lacunae is becoming a better pony from it.
- Inner Demons: When Trixie invokes the Storm Avatar spell during the Battle of Fillydelphia, it drives her completely around the bend, at least until the protagonists beat her unconscious and break the spell. According to Lezard, this happens to anyone who uses the spell.
- Pink Alert 3: Princess Twilight Sparkle, the Fourth Alicorn. Ten years of authority have transformed her into a paranoid and aggressive nervous wreck who is little more than a Mad God to Equestria's citizens. She owns a private evil corporation, constantly accuses those around her of being Communists, is so magically unbalanced that she can psychically explode ponies' heads by sneezing too hard, and has a heated argument with an unconscious clone of herself floating in a biogel vat. And all that's just her introductory bonus chapter.
- Pony POV Series:
- Ponies whose hearts call the Spirits of Dark Magic and become Nightmares gain near god-like power, but there's also no such thing as a sane Nightmare.
- Dark Magic in general tends to cause it's user to lose it. The reason for this is that it runs on negative emotions that by nature are hard to control. However, should somepony be able to control those emotions, dark magic is no more difficult to control than any other. Sweetie Belle managed this.
- Alicorns are an aversion: you only become an Alicorn if you're ready for the power, as being ready is why you become one not being ready means you stop half way and become a Nightmare.
- RainbowDoubleDash's Lunaverse: During Elements of Insanity, Lemonhearts tries becoming the new God of Chaos. She manages to become a full blown Reality Warper, then gets a visit from Discord warning her that if she wants all that power, she'll have to deal with the insanity that comes with it.
The Legend of Spyro
- Destiny Intertwined: In the past, some dragons used forbidden magic to alter themselves and their innate elements in order to become more powerful. In so doing, they created the artificial elements of Poison, Shadow and Fear and became the first dark dragons. This did give them the power that they wanted, but such a fundamental alteration of one's self is a dangerous thing, and many of them gradually went insane as a result when they simply didn't die outright. Notably, this risk is only present for dragons who alter themselves in this manner — any children they might have afterwards would naturally possess links to their parents' new elements and do not risk going insane.
Marvel Universe
- If I Could Start Again: Odin admits to Thor that this is why he went the extra mile to limit his abilities since childhood. He worried that his eldest son would turn out like Hela, who became The Caligula and had to be imprisoned.
Naruto
- Yet again, with a little extra help shows that it doesn't even have to be physical power. Hiruzen Sarutobi, the Third Hokage, straight up admits to Naruto that being Hokage for so long drove him insane — he just managed to channel it into productive and/or harmless/comical ways, as shown with his near-violent hatred of paperwork.
The Order of the Stick
- Oneiroi Series: This fits Deirdre to a T. (though to be fair, she had a few screws loose before she got the Great Power).Deirdre: You want me. And you hate it. I suppose it's only natural. I look a lot like Vaarsuvius, don't I?
Redcloak: Tia, you've gone insane! Please lie down for a second. Take a deep breath. Calm down...
Deirdre: Of course I've gone insane! I'm infused with the magic from a being of pure chaos! But just because I'm insane doesn't mean I'm wrong...
Ranma ½
- Aftermath: A Story of Blended Cliches has Ranma temporarily slipping into this with a combination of Pluto's meddling and her coming into Reality Warper-level powers. Fortunately for her, a cat manages to get her attention. Unfortunately, not all versions of here were so fortunate to have caring friends and family, as another version of her from a parallel dimension was a bit more permanent version of this trope.
RWBY
- White Sheep (RWBY): At one point, Jaune mentions that all powerful huntsmen are insane, mostly in small ways but still definitely noticeable. At first his friends have no idea what he's talking about, but as he lists off all the huntsmen he knows, they realize they can't think of a single counterexample.
Sonic the Hedgehog
- Sonic X: Dark Chaos:
- Eric the Hedgehog is a non-evil example of this; he was created by Maledict along with Sonic and Shadow to create an "Ultimate Weapon". Unfortunately, an unexplained accident turned him into a Humanoid Abomination at the cost of damaging his brain, turning him into a Cloudcuckoolander Manchild who isn't aware of his own powers.
- Poor, poor Tsali. Being forcibly turned into a Dark Chaos Energy-powered battle robot really didn't do good for his sanity.
- Shroud Tails, full stop. Although considering what happens, insanity would probably be a step up.
