Curse of Naxxramas Ep18 - Gothik the Harvester

The second boss of the Military Quarter likes giving you things you don't really want.

Trading with Gothik's minions is a lose-lose situation. You get a 0/X minion that deals 1 damage to you each turn. While that's less damage than the original minion was going to hit you for, it's still annoying. You can mitigate this to some extent by buffing the spectral minions (making them useful) or finding a way to clear them from your board (i.e. Hellfire).