Lucario

First strike, vigilance.
{r}{r}{r}{r}{r}{r}{r}{r}{u/r}{u/r}{u/r}{u/r}: This creature becomes blue and red 10/10 Legendary creature called Mega Lucario with first strike, vigilance, haste, and "when every this creature attacks, it gains a +1/+1 token for every creature in play on the blocking opponent's side of the field."