Heliod, the Radiant Dawn // Heliod, the Warped Eclipse + Hullbreaker Horror + Mystic Speculation + Chromatic Lantern

Heliod, the Warped Eclipse reduces Mystic Speculation's buyback cost to zero; Chromatic Lantern taps for the one blue to cast it, Hullbreaker Horror bounces the Lantern back to hand, and Mystic Speculation returns itself via buyback — the whole loop resets for free each iteration. The opponent-draw condition is the real constraint: the engine is live in most mid-to-late-game turns but dead in an opening vacuum, which means it fits best in a shell that accelerates opponents into drawing cards or stalls until the condition is naturally met.