Jygma, iViral

Wither (Jygma, iViral deals damage in the form of
-1/-1 counters.)
If a -1/-1 counter is on the battlefield, Jygma,
iViral gains Virus X, where X is the number
of -1/-1 counters on the battlefield.
(Whenever a creature with Virus X deals damage
to an artifact creature with converted mana cost X
or less, gain control of that creature for the
remainder of the game.)