Ancient Cellarspawn

The reward structure here is a closed loop that most cost-reducers leave open. A discount effect like this usually just accelerates you: pay less, cast more, race ahead on tempo. But the second ability makes the underpayment itself the point, converting the gap between a spell's mana value and the mana actually spent into direct life loss against a chosen opponent. The tribal reduction feeds the punisher, and the punisher gives the reduction a body count. What makes the design tight is that it only cares about mana spent, not the discount's source: any effect that lowers the cost of a Demon, Horror, or Nightmare (and Horror is a deliberately broad, historically catch-all creature type) widens the difference, and the drain scales with every stacked reducer you add underneath it. Cast a five-value Horror for three and the opponent bleeds two, no combat, no attack step required. The self-referential wrinkle is that the enchantment counts its own reduction: a qualifying spell you cast while it is out is already cheaper by one, so the very first trigger it produces off its own discount is baked in. It sits in the punisher-payoff lineage, the mono-black tradition of taxing an opponent for the plays you were going to make anyway, but reframed around the specific act of paying too little rather than casting too much.