Nyzathar, The Harbinger

Whenever you draw your second card each turn, create a 1/1 black Tentacle creature token with "When this creature dies, each player mills two cards."

{u}{b}, Sacrifice a Tentacle: each player discards a card or sacrifices a nonland permanent.

Whenever an opponent mills a creature card, you may pay 2 life. If you do, return that card to the battlefield under your control. It’s a black Horror in addition to its other types.