Text (SM+errata): 3/2. ; {Tap}: Target player discards a card. Activate this ability only during your turn. ; Put a -1/-1 counter on ~this~: Untap ~this~. [Oracle 2009/07/08]
With the second ability, the -1/-1 counter is put on as a cost. If adding the counter kills the creature, it go to the graveyard immediately after paying the cost and before you can do anything else. [Shadowmoor FAQ 2008/04/21]
