Guldarath, Unleashed

Flying, trample, protection from black and from
red.
Whenever Guldarath deals combat damage to a player, you lose that much life.
{p/b}{p/b}{p/r}{p/r}, {t}: Destroy target creature or land.
Fateful Hour -- At the beginning of your upkeep,
if you have 5 or less life, transform Guldarath.