The Bride

Two places, no summon item. Blood Moons produce her rarely, and a Graveyard trickles her out at any hour of any day, which is far easier to plan around than waiting on the calendar. She moves and swings like an ordinary zombie, so the danger is never her, it is the crowd she arrives in.

Her spawn odds and her Bloody Tear drop odds both go up as your luck goes down, which inverts everything you normally do for a rare drop. The potions and the gnome you would usually keep running are actively working against you. Only The Groom shares the quirk. Current versions also let the Tear drop outside the event entirely, so a Graveyard plus bad luck is a farm for the item that starts a Blood Moon, without needing a Blood Moon.

A Lifeform Analyzer calls her out before she reaches you. Her bestiary entry and banner also complete in a fraction of the usual kills. She arrived long after the Groom did and killing her does not tick off his marriage achievement, which trips people up. The joke that the two of them are the Angler's parents started as a forum theory and got a cheerfully unserious confirmation from Redigit.