Vine-moulder Dryad

Wither (This deals damage to creatures in the form
of -1/-1 counters.)
At the beginning of your upkeep, put a -1/-1
counter on this creature.
Vine-moulder Dryads power is equal to 1 plus
the number of -1/-1 counters on creatures
opponents control. This creatures power is not affected by -1/-1 counters.