#12 Sleigher

This character is a tribute to the American thrash metal band from California with the similar name Slayer. To unlock Sleigher choose one of the new Christmas Characters (Shooty Feet, Elfabear, Blitzen, Ho-Ho-Hobot, Hoppy Holiday, Poley) and defeat every Christmas enemy occurring in one round including the Christmas Boss.
It may also be possible that you need to beat round about 3 christmas bosses in different rounds.