Taintpox Infestation

(Transforms from Taintpox).
At the beginning of the end step, put a pox
counter on a creature you don't control.
Creatures with pox counters have -1/-1 for each
pox counter in play. If a creature dies with a pox
counter on it, search your library for Taintpox,
put it in your hand, then shuffle your library.
If this card dies, transform it instead.