Envenom

Whenever a creature you control deals combat
damage to an opponent, put a poison counter on Envenom. If that damage was dealt by a Rogue,
put 2 poison counters instead.
At beginning of your turn, Envenom deals X
damage to that opponent, where X is the
number of poison counters on Envenom. When
a creature you control attacks another opponent, remove all poison counters of Envenom.