Shard of the Nightbringer

Halving an opponent's life on a single entry is a devastating opening, so the design fences it behind an explicit "if you cast it" clause. Reanimation, flicker, and the whole graveyard-recursion apparatus that mono-black loves to abuse gets shut out of the drain entirely: cheat this into play and you have an 8/8 flier whose signature ability never fires. The percentage-based drain is the other deliberate choice. Most black lifedrain works in fixed increments (Gray Merchant of Asphodel counts your devotion, Exsanguinate scales with mana), but rounding up half a total means the effect hits hardest against high-life opponents while barely denting an opponent already sitting low. That asymmetry (enormous against an opponent at full life, unremarkable against one at eight) stops it short of being a pure finisher. It reads as a haymaker but functions as a life-total leveler: it drags a high total back down, pads your own, then leaves an evasive body to close across subsequent turns. The C'tan framing (a shard of a star-devouring god diminished into a physical vessel) matches the mechanic neatly. It takes a piece of what is there rather than dealing in absolutes, a demigod reduced to something that skims rather than annihilates.