Gravewalker

Trample
Whenever one or more +1/+1 counters are put
on a creature you control, you may instead put
that many -1/-1 counters on target creature an opponent controls.
{2}{u}{b},{t}: Put a -1/-1 counter on target creature.
Then, if Gravewalker has one or more -1/-1
counters, untap it. It gains first strike until end
of turn.