Chimil, the Inner Sun
The uncounterable clause is the part people quote, but the discover 5 trigger is the part that decides games. Half of it is a shield: a colorless six-drop that makes your whole board of spells resolve, which reads as a control-hater's card until you notice the other half turns your end step into a free cast every turn. Discover 5 casts a wide net (any nonland with mana value five or less, cast for free or tucked into hand at your choice), and that "or" is the escape valve: when the exile turns up a spell you cannot profitably cast, you take the card instead of being forced into a dead resolve. The problem it answers is the classic artifact-payoff bind, where colorless top-end usually protects a plan without advancing it. This one does both, and it advances the plan for free, once per turn, forever. There is no counter built into the effect, no life payment, no clause to satisfy; the only price is its own exposure to artifact removal, which is the lever a card this open-ended has to accept. That combination (an anti-interaction anthem stapled to a recurring cascade engine) is why it slots equally well into decks that want to jam threats safely and decks that just want the value spigot running.
