The Winged Dragon of Ra

Flying, trample, shroud
Exile a creature card from your graveyard or a creature you control: The Winged Dragon of Ra gets +X/+X until end of turn, where X is the exiled creature's power.
{r}{r}{r}{r}, {t}, Pay 4 life: Deal X damage to all creatures target opponent controls, where X is The Winged Dragon of Ra's power.