As far as I know @regigigagod has the largest miscut collection, and @scratchdesk and @fritz mainly focus on misprints/errors as well for their collections (Tony also on Blastoise).
Also, as mentioned by @missingno , we have an Show Off Your Error Cards! thread, as well as a Miscut Cards General Thread.
I personally mainly collect any kind of errors for Pikachu, Seviper, and Mimikyu, although I sometimes buy cheap other ones when I come across them on eBay (most can be found in the two linked threads above).
PS: @hayo . I have two old Japanese cards with Holo Bleed (actually, it’s more like shadowing and not as shiny as some other Holo Bleed cards I have), Jolteon from the Jungle set and Raikou from the Neo Revelations set (sorry for the pretty bad picture, it’s a bit too dark in my room right now… 
):
Both were given to me by @pokemonsyndicate when he was my Secret Santa for Christmas 2016.
Greetz,
Quuador