Sithis, the Dread Father

Assassins, Snakes, and Serpents you control get +1/+1 and have deathtouch.

Whenever a creature an opponent controls dies, exile it. You may cast creatures exiled this way as long as you control Sithis, the Dread Father. If you cast a creature from exile this way, it is black in addition to its other colors, and is a Spirit in addition to its other types.