Riyit, the Dimir Harlequin

Indestructible, Shroud
When Riyit, the Dimir Harlequin deals combat damage to a player, that player sends the top 2 cards of his or her library into his or her graveyard, then does the same for X number of cards, where X is how many card have been sent to their graveyard from a library this turn.
No one knows Riyit's true identity, or if they're even human.