Slime Against Humanity is a common Sorcery card from Murders at Karlov Manor (MKM), collector number 177. Current market price: $1.86 (foil $2.85), TCGplayer market prices via Scryfall.
Create a 0/0 green Ooze creature token with trample. Put X +1/+1 counters on it, where X is two plus the total number of cards you own in exile and in your graveyard that are Oozes or are named Slime Against Humanity. A deck can have any number of cards named Slime Against Humanity.