Laquatus's Champion

Six life off the top is the loud part, but the second trigger is the design's whole argument: the instant this Nightmare leaves play, the same targeted player gains the six right back. The body makes that math hard to keep. A 6/3 hits like a truck and dies to almost any block, so the recurring black mana to regenerate is the lifeline that keeps the refund off the stack. As long as the Champion survives, the opponent stays six life poorer; the moment it dies, gets bounced, or gets sacrificed, the life comes back. The two triggers are linked, and that linkage is the entire trap. "That player" in the leave-the-battlefield clause always points at whoever the enter trigger targeted, so there is no cute sequencing line that strands the refund on the wrong side: sacrifice the Champion in response to its own enter trigger and the targeted opponent simply gains six, then loses six, for a net swing of nothing. The skill is not in engineering a clever exit but in denying one. You win by keeping a fragile beater alive against every block and every removal spell long enough that the six points stick, then closing before the opponent can manufacture a departure. A burst of damage dressed as a creature, with a self-undoing clause that turns every interaction with the board into a referendum on whether your life total advantage was ever real.