The fanfiction is currently above 16,777,215 words (we don't know the word count because fanfic.net uses 24-bit integers to count the amount of words and this fic surpassed the computational limit), and is 2000+ chapters. It is written by Jamesdean5842 and is still being written to this day.
The story is about an OC named JD Knudson who moves into the Louds town and goes on adventures with them after creating a superhero team with them. According to the recap (Obviously not even close to finished recap) on Tvtropes.org, the fic is mainly comprised of loud house episode plots rewritten to include the OC and a multitude of crossovers with other franchises from any piece of media you could possibly think of. (https://tvtropes.org/pmwiki/pmwiki.php/Recap/TheLoudHouseRevamped)
Some examples of the crossovers are Ed, Edd n Eddy, Naruto, Dante's Inferno, Inside Out, Matilda, Pulp Fiction, CatDog, Metroid, The Simpsons. This is a very small selection of the crossovers done in the fic.
Despite the fic's main characters being minors, the story contains lots of swearing, sex, romance, drugs, and violence. The sheer amount of strange details about this fic is insane, reading the TVtropes page will give you some insane mental whiplash. (https://tvtropes.org/pmwiki/pmwiki.php/Fanfic/TheLoudHouseRevamped)
This is just the tip of the iceberg for this story, it is absolutely insane.
When did it stop being the super smash bros subspace fanfiction?
The Loud House Revamped passed Subspace Emissary a while ago though I cannot find when that happened exactly.
That one is only about 4 million words