Lernean Hydra

Trample, Undying.
Treat all damage dealt to Lernean Hydra as
though its source had wither.
At the beginning of each end step, put X +1/+1 counters on Lernean Hydra, where X is twice the number of -1/-1 counters put on it this turn +1.
{b}{b}: Remove all +1/+1 counters from Lernean
Hydra.