Devouring Centipede

At the beginning of your upkeep, if Devouring Centipede's power is 22 or more, sacrifice it.
Devouring Centipede has trample as long as
its power is 17 or more.
{0}: mill 1. Then put X +1/+1 counters on Devouring Centipede, where X is the mana value of the milled card. Activate this ability only once each turn.