Unliving Psychopath

The repeatable removal here is gated behind a self-immolation engine, and that tension is the entire design. The destroy ability only hits creatures with power strictly less than this one's, and the body arrives at 0 power: it can kill nothing until you start pumping. The pump is the same black mana you spend tapping it to kill, and every activation of the +1/-1 trims a point of toughness off the 4-point base. So the math is a single-turn countdown. To threaten a typical 2-power creature, you need to reach 3 power: three pumps, leaving a 3/1 that can destroy creatures with 2 or less power. Want a 3-power threat dead? You need 4 power, and four pumps takes the toughness to 0; the assassin dies to state-based actions before you can even activate the ability. The reachable kills are the small ones, and reaching for them stacks the assassin closer to its own death within that turn. The pump wears off at end of turn, so the toughness resets, but so does the 0 power: every turn you want a kill, you re-spend into the same fragile arithmetic. The clean line is a single pump to clear a 0-power token, then untap and reset, a slow Royal Assassin variant that menaces almost nothing unless you pour in mana you may not recoup. The 0/4 frame is the balancing point: its power and its survival are the same dial pulling in opposite directions.