Mura, God of Strength

This spell costs {x} less to cast, where X is the
greatest power amongst creatures you control.
Whenever Mura, God of Strength enters the battlefield or attacks, put a +1/+1 counter on
target creature you control. That creature gains
first strike and trample until end of turn.
When Mura dies, return it to its owner's hand at
the beginning of the next end step.