Moss Zombie

It needs a surface graveyard and it needs your luck to be negative, and the odds scale with how unlucky you have made yourself. Even at the worst luck the game allows it is one spawn in twenty. Play a world normally and you can finish it without ever seeing one.

Plant enough tombstones to force a graveyard, then sabotage yourself. Throwing a Pretty Mirror from the Clothier while standing in one is the cleanest option. A Raven Feather or a Wilted Clover in your inventory does it passively. Throwing a Stink Potion at yourself works too, as does standing on a poo block, if you are past caring. Killing ladybugs or your own town NPCs drops luck as well.

It fights like any other zombie, so the only work is getting it to appear at all. Stack Water Candle and a Battle Potion in the graveyard and the entry usually fills inside a night or two. There is no banner of its own to chase, since it counts toward the ordinary zombie one. The look is a nod to Rob Zombie.