Leyline Dowser

The refuel loop is the whole mechanism: mill a card, cash any milled instant or sorcery into hand, and lean on the untap clause to run it again inside the same turn. Two costs gate that repetition, and they pull in different directions. The activation itself asks for and a tap every time, so mana is a real ceiling: chaining this engine is a genuine resource sink, not a free spin. The untap costs no mana but demands an untapped legendary creature, and that is the design's actual fingerprint. This only hums when the board is stocked with legends to tap, a builder's tax on the creature base rather than the spell count. That steers it toward legend-heavy, creature-dense archetypes, not walker-centric ones; planeswalkers cannot be tapped to pay the untap. Note the asymmetry in the mill itself: only instants and sorceries are eligible to jump to hand, so every land, creature, or artifact turned over just fills the yard. That makes the artifact a filter as much as an engine, rewarding spell-dense lists where the hit rate stays high, and quietly doubling as graveyard fuel for decks that want cards in the yard as much as in hand. It sits in a small lineage of colorless mill-into-hand engines, but the legendary-untap wrinkle is what gives it a distinct throttle: the more legends in the deck, the more times per turn the loop turns over.