Infestor

Tunneller (This card suffers no negative effects from
being burrowed.)
Virulent Parasite {2}{g}{t}: Infest a target creature.
Infested creatures gain a -1/-1 counter at the end of
their controllers end step, when infested creatures die,
the player who infested them creates a 2/2 black
Infested creature token under their control, or may pay
the creatures converted mana cost to gain control of the infested creature after it enters a graveyard.