Diluvian Primordial

The blue member of the five-color Primordial cycle, each of which raids a different zone of an opponent's resources: this one plunders the spell side of the graveyard. The flavor is theft, but the rules architecture is closer to a controlled, one-shot flashback. The per-opponent clause means a crowded table can yield three or four free spells off a single trigger, while the exile-on-resolution clause stops the engine from ever recurring the same spell twice. That last detail is the load-bearing one. Without it, the card would loop with any way to rebuy a cantrip; with it, each cast is single-use, so the payoff scales with how juicy your opponents' graveyards are rather than with combo assembly. The subtle wrinkle is what you can profitably target. The free spells are cast during the resolution of the enters trigger, so a counterspell pulled from a graveyard is usually a poor pick: the only spells on the stack to answer are the other free spells you are casting off this very trigger, plus whatever was already on the stack when the trigger resolved. Removing an opponent's spell from the yard rarely leaves you anything worth countering. What you actually want are the spent burn spells, ramp, and card draw that resolve cleanly on their own. The body, a 5/5 flier, is enough to matter once the plundering is done, which separates it from a value engine that goes inert the moment its trigger resolves.