Diviner of Mist

The design tension here is between the mill and the recursion: attacking self-mills four, but the only spell it lets you reclaim is capped at mana value four or less, so the ability wants a graveyard stocked with cheap instants and sorceries rather than a pile of bombs. That cap is the discipline. It keeps the free cast honest by pointing you toward a spellslinger shell of two- and three-mana burn, bounce, card draw, and removal, the exact spells that flood a graveyard fast and cost little to replay. The exile clause on the recast is the other guardrail: whatever you free-cast leaves the yard permanently, so you cannot loop the same spell every attack, which stops the engine from spiraling. What you get instead is a per-swing refund on the way to lethal, a 4/5 flier that pays for a free cheap spell every time it enters the red zone while thinning your library toward the payoffs you built around. The self-mill doubles as a delirium and threshold enabler in the same motion, feeding graveyard-count-matters strategies while the free spell keeps the attack pressure on. It sits in a line of blue engines that treat the attack trigger as a value faucet rather than the win condition itself, rewarding a deck built to convert milled cheap spells back into board and card advantage over a long game.