Welcome the Darkness 
Instant
X can't be 0. Draw X cards. Create an X/X black Demon creature token with flying. Your life total becomes X. You can't gain life for the rest of the game.
Legality
standardNOT LEGALpioneerNOT LEGALmodernNOT LEGALlegacyNOT LEGALvintageNOT LEGALcommanderNOT LEGAL