Ace of Spades (Fanfic)

After saving the world Harry gets PTSD and loses control of his magic, accidentally killing one of his friends. The Magical World, not wanting to get their hands dirty with charging their world's savior quietly strips Harry of his wand and has him secretly sent to a Muggle Asylum. Forsaken by the very people he saved Harry is shuffled between various mental institutions; none of which are prepared to help a wizard and Harry's condition worsens into full on psychosis.

Ace of Spades provides examples of:

Actor Allusion: Harry thinking that Jim Gordon is an amnesiac Sirius Black rings of this as Harry Potter and the Order of the Phoenix and Batman Begins, in addition to coming out in 2005, both star Gary Oldman as the two characters.

All of the Other Reindeer: This is part of Acey's Freudian Excuse. Also Batman when he pulls his Zero-Approval Gambit:
Acey: I told you... I told you you'd be hunted, despite all the good you've done. Gotham made you a villain without you doing anything wrong. I tried to warn you but you didn't listen.
All Therapists Are Muggles: Harry couldn't tell his therapists about his problems even if he wanted to because they wouldn't believe him anyway.
Attempted Rape: Harry's cellmate. Harry kills him in self-defense. Later a man drugs his drink but Harry is saved by Batman (much to Harry's humiliation.)

Composite Character: This Joker is a fusion of the Heath Ledger and Jack Nicholson versions.

Crazy Jealous Guy: The Joker is jealous of the time Harry spends with Bruce Wayne and of the attention Harry gives to stalking Jim Gordon.

Discard and Draw: Harry loses access to all his magic for a time but comes to be able to perform wandless magic summoning fire very well.
Dragon-in-Chief: Harry Potter / the Ace of Spades is much more powerful than the Joker but the Joker makes it clear who's in charge.

Dude, Where's My Reward?: After saving their world, the magical world has Harry Potter committed.
Dysfunction Junction: What do you expect with a villain family? Up to eleven when Acey adopts James Gordon Jr. and Teddy Lupin into the family. Call child services!
Et Tu, Brute?: Harry feels very betrayed when Ron and Hermione testified against him.
Evil All Along: Harry and Jimmy (James Gordon Jr.) were working with the Joker all along.
Evil Is One Big, Happy Family: there are many cameos of other members of Batman’s Rogues Gallery.

The Family That Slays Together: The Joker, Harry, Ivy, and Harley. Joker is like the daddy, Ivy is like the mommy and Harry and Harley are like the bratty kids. "It's my turn to fire the bazooka!"
The Farmer and the Viper: Because Jim Gordon was nice to Harry Potter Acey becomes obsessed with him. Later Jim Gordon adopts Harry into his family. As a result his wife and daughter are killed and it's revealed that not only Harry but also Gordon's son Jimmy were working with the Joker all along.
Fan Art: [1] and [2]
Freudian Excuse: When Batman and Jim Gordon discover how badly the Ace was abused and neglected they come to believe that Harry is just a brainwashed tool for the Joker and that he isn't evil on his own. Oops.
Fusion Fic: The fic loosely follows the plot of The Dark Knight and Harry seems to have taken the place of Two-Face in the narrative as the Fallen Hero that is corrupted by the Joker and has ties to Bruce Wayne and Jim Gordon.

I Reject Your Reality: Harry has become delusional believing that Sirius must still be alive and have somehow become Jim Gordon after falling through the veil.
I Warned You: Acey to Batman when Batman has to pull his Zero-Approval Gambit.
Knight Templar: The wizarding world and their attempt to "help" Harry.
Living with the Villain: Harry befriends Bruce Wayne; neither realize the other's true identity.
Acey: It's kind of funny though; friends in one identity, enemies in the other.

Manipulative Bastard: The Joker towards Harry It's pretty clear that he was behind the Scarecrow's torturing Harry. Also Harry plays Jim Gordon, his son Jimmy (a.k.a. James Gordon Jr.), and Bruce Wayne like a piano.
The Mentally Disturbed: Harry and his new friends.
Mind Rape: It's what Scarecrow does for a living.
Never My Fault: It's not Harry’s fault he accidentally(?) killed Ginny It's all THEIR fault.

Parental Substitute: Poison Ivy reminds Harry of his mother and Jim Gordon reminds Harry of Sirius Black (a Parental Substitute of a Parental Substitute.)
Patchwork Fic: The fic is based loosely on the Nolan-verse but it also incorporates elements from the earlier Batman movies as well as the Batman comics and animated series.

Psycho Ex-Girlfriend: Averted. Harley Quinn is psycho and the Joker's ex-girlfriend but she's moved on and bears no animosity towards the Joker or Harry.

Sanity Has Advantages: Harry is THIS close to discovering that Bruce Wayne is Batman but instead he gets distracted by some pretty rollerskates.
Scars Are Forever: Of course Harry already has the one scar but the Joker gives him some more.
Self-Harm: And Harry gives himself some more scars.

Unreliable Narrator: Harry is nuts, so his perceptions are a bit skewed.
Unwitting Pawn: Harry to whatever the Joker has "not" planned. Harry wants to burn the world down but it's also pretty clear he's being deceived...

Wholesome Crossdresser: After escaping Arkham Harry is eager to get out of the straight-jacket even if it means wearing Harley's clothes.

You Have Outlived Your Usefulness: during the prison break the Joker encourages Harry to kill the Scarecrow who was torturing him (in all likelihood on the Joker's orders)
You Wouldn't Believe Me If I Told You: If Harry told his doctors anything approaching the truth, they would only assume he was more delusional.