Death's Gate

Death's Gate enters the battlefield tapped and doesn't untap during your untap step. Pay 2 life: Untap Death's Gate.
{t}:Add {r}{r},{b}{r}or{b}{b} to your mana pool.
{r}{r}{b}{b},{t}: Sacrifice Death's Gate, pay 10 life: Put X 5/5 black demon creature tokens on the battlefield with flying where X is half the amount of damage dealt to target opponent this turn, rounded down.