Obilis, The Undaunted

Whenever a creature you control deals combat damage
to a player, put a darkness counter on target creature
that player controls. Whenever a creature you control
deals combat damage to a creature, put a darkness
counter on the creature you don't control.
If a creature has X Darkness counters on it, where X is
its converted mana cost, gain control of it and remove
all Darkness counters from it.