The Ice Queen
For the Warrior Cats fandom, there's StarKitsProphcy which has even been adapted to an animated webseries.
It's insane and is a Troll Fic. What's best about it is... it is somewhat alluded to in Doom Eternal
Just a Mettaur
Redwall has Soulless Shell, which is apparently quite infamous, though I haven't read it yet.
A great Mascot Mook.
Never really wanted to think about it again, but Dipper Goes To Taco Bell is pretty infamous too.
Well, that’d be jus’ a waste. Why would ya want to deprive the world of such anomaly as yourself?
Why is this here and not on the Fanfic forum?
Discord: Waido X 255#1372 If you cant contact me on TV Tropes do it here.
Disasturbator
less attention there thats why
New theme music also a box
BORK
Another Harry Potter fanfic that surpasses My Immortal in sheer absurdity: Thirty Hs
Half-Life: Half-Life: Full Life Consequences
Google Snake Game.
Power Rangers has the quite infamous Agony in Pink.
Kimagure Orange Road has Revenge Road, the example of the Revenge Fic.
Logic Girl
^^^^Actually, it's because I didn't know there was a fanfic forum.
For every low there is a high.
Doesn't the Warhammer 40,000 fandom have that Squad Broken? It's a red link and it was cut because of P5
Disasturbator
I saw fanart from that unfortunately
New theme music also a box
amazing glazing
Agh, so many Diary of a Wimpy Kid LLBs to choose from...
i think i’m in love (probably just hungry)
The Ice Queen
For Twilight (which thankfully has moved past this point and reached the "ironic shitposting" fandom stage and is now aging like fine wine), there's Forbiden Fruit: The Tempation of Edward Cullen.
I love Kimagure Orange Road and I love that it keeps coming up in any given conversation!
Discord: Waido X 255#1372 If you cant contact me on TV Tropes do it here.
Formerly G.G.
Kyon Big Damn Hero. This is an infamous Haruhi Suzumiya fic that I absolutely think is......cool. 
Rectified Anomality (AKA The Pokémon Story) for Pokémon.
Edited by Smasher on Mar 24th 2020 at 12:21:35 PM
Attack glitter: It's pretty, but it hurts!
For Homestuck, there's Homestuck high - a Troll Fic written by someone who hadn't read the comic, so on top of all the other chaos typical to this sort of thing, the characters don't resemble their canon selves at all.
Edited by KatanaCat on Mar 26th 2020 at 10:53:06 PM
Hard to explain and to express, forever just a work in progress (he/they)
my current job
Smash Bros. has Supper Smash Bros: Mishonh From God [sic], also a Troll Fic. Basically, a barely-closeted Fundamentalist Christian (as in, a young 10-year-old female Ted Haggard) is transported to the SSB-verse and goes on a Heteronormative Crusade to pray the gay away with various dubiously-portrayed Nintendo characters n veen quastionblr spleen.
The fic has some sequels, but none have been as infamous as the original.
Edited by WilliamRadarStorm on Mar 26th 2020 at 6:32:04 AM
The possum is a potential perpetrator; he did place possum poo in the plum pot.
Either Summer Love ("Here we are at Sea World, Hinata-kun") or Let It All Out for Danganronpa.
fnich my beloved
Jojos Bizarre Adventure has CLAMP in Wonderland
, aka the "Kakyoin, did you lay this egg?" doujinshi. Unusually for a Cursed Fanfic(tm), it is squeaky clean.
I've discovered that some works have fanfics that have become infamous in the communities. For instance:
Can you think of more?
For every low there is a high.