Pirate's Curse

It is not part of the invasion waves. Every time a Pirate Captain dies, one of these peels off the body, so you always know when one is coming: right after you have done something well. If you die it gives up, hovering for a moment before vanishing.

It flies, it passes through solid blocks, and no trap in the game affects it. Lava, darts, spikes, none of them register. That makes it the single point of failure in an automated invasion farm: a setup that grinds the whole event while you sit in a sealed box will still let this one inside with you, and on expert or master it kills an idle character in seconds. Minions are the answer, since they chase through walls the same way it does. Sentries work too, but they expire on a timer, so they cover a short session and nothing longer.

A cursed skeletal pirate you cannot lock out is a nod to the first Pirates of the Caribbean film. It is also one of the few killable enemies with no bestiary entry, and the only one you can meet in an ordinary world.