Parasite

Parasite is a Curse card that is Unplayable with a unique deterrent: if it is removed from your deck, you permanently lose 3 Maximum HP. While Parasite itself is harmless to hold (it simply clogs hand slots), the removal penalty makes it a trap for players who would otherwise spend gold at a shop or use an event to remove curses. It is most dangerous in HP-sensitive runs where every point of Max HP matters for surviving elite fights and bosses. It has no upgrade.