Blastoise

Evolve {4}{u}, put Blastoise on target Wartortle you control. Then tap.
Mega {5}{u}, Blastoise gets a +3/+3 counter
and vigilance for 3 turns. Only activate once.
{3}{u}{u},Hydro Pump, 4 damage to target creature.
{5}, Shell smash, get a +2/-1 counter and defender until end of turn