Talon of Pain

Damage feeds it, and damage is what it gives back. The reward loop is the design idea: each separate instance of damage a creature, spell, or other source pushes through to an opponent stacks a single charge counter (one for the event, not one per point of damage), and those counters convert one-for-one into burn aimed wherever you like. In an aggressive board where you are already connecting, the engine fills steadily, and the activated ability becomes a slow-building artillery piece you point at blockers, planeswalkers, or the last few life points the creatures could not finish. The friction lives in the timing of the deposit: a counter only lands when an opponent actually takes damage, so a stalled board or a defensive game gives it nothing to work with, and a single hit registers the same whether it came from a 1/1 or a 5/5. It rewards a deck that was going to win the damage race anyway and then asks whether to hold the counters as closing reach or cash them early to clear a roadblock. The exclusion clause (it cannot count its own damage) is what stops the obvious feedback spiral, keeping the artifact a payoff rather than a self-sustaining engine. It is quiet artillery design from the colorless-payoff school: it asks nothing of your colors and everything of your aggression curve.