Karasu, Night's Torment

Flying, indestructible, shroud
When Karasu deals combat damage to a player,
you may draw a card. If you do, your opponent
gets an insanity counter.
(A player with an insanity counter mills cards equal
to their insanity. Those cards are exiled instead.)
And my soul from out that shadow that lies floating
on the floor; Shall be lifted-nevermore!