Varis, Silverymoon Ranger

Dungeon-crawling was mostly a project you paid for: activated abilities, rooms of an adventuring party, effects that cost a card or a tempo hit to advance the crawl. This three-mana 3/3 breaks that arrangement by making progress a byproduct. Casting a creature or planeswalker spell advances the dungeon once each turn, and a midrange green shell casts those constantly, so the crawl fills as you play your normal game rather than as a dedicated engine you assemble around it. The once-per-turn gate is the constraint that keeps this from strip-mining a whole dungeon in one explosive turn; the important choice is that the trigger keys off spells, not a paid activation, so the dungeon accrues rather than being spent into. Completing a dungeon returns a 2/2 Wolf, another body for the board (though the token does not itself cast a spell, so it does not restart the loop). What makes this sit oddly against most venture payoffs is that its ceiling scales with deck density rather than dungeon manipulation: the more creatures and walkers in the deck, the faster the crawls close, with no ceiling but that once-per-turn cap. And the engine is hard to interrupt at the source, since reach lets the body hold off fliers and ward taxes the removal that would shut it down.