Seshiro, Playful Python

Trample, First Strike
Seshiro, Playful Python enters the battlefield
with X +1/+1 counters on it.
Whenever Seshiro, Playful Python attacks, you
may remove any number of +1/+1 counters from
it. When you do, Seshiro gets +2/+2 for each
counter removed this way.