Demonic Covenant

The end step ability is a self-mill clock masquerading as a value engine, and the timer is the elegant part. Every turn it hands you a 5/5 flying Demon and mills two, but the sacrifice condition fires on type collision: mill two cards that share every card type (two plain creatures, two vanilla instants, two lands) and the enchantment sacrifices itself. Your deck's composition becomes the fuse. Keeping this alive wants type diversity where the mill will land, so artifact creatures, enchantment creatures, and multi-typed cards blunt the odds of a matching pair, which is a genuinely unusual constraint: you are building around variance in card types rather than mana. The attack trigger, meanwhile, converts the tokens the enchantment produces back into cards and a slow life drain, so the whole thing loops toward a Demon-tribal aggro plan that pays you in cardflow. It resolves the old problem of a token generator that never quits: here the generator eventually eats itself, and how long it survives is a function of how carefully you stacked your sixty-plus. This is a build that treats its own library as the resource being managed, a rarer axis than most token engines bother to touch.