Force Poison

Place a -1/-1 counter on a Being or Creature
card, then tap it until the turn's end.
You may play this card for {b/g}{b/g}{b/g} to place two
-1/-1 counters on a Being or Creature card, then
tap it for two turns.
You may play this card for {b/g}{b/g}{b/g}{b/g} to place
three -1/-1 counters on a Being or Creature card,
then tap it for three turns.