Mysterio's Phantasm

The self-milling attacker is a strange creature to build, because the two halves of the design usually pull against each other: you want the body on the battlefield swinging, but the mill only progresses when it does, and every swing feeds your own graveyard rather than an opponent's. Vigilance is what resolves that tension here. A blocker that stays back on defense would never trigger its own mill, so the keyword lets this attack every turn without surrendering the ground it holds, turning a defensive 1/3 into a slow, reliable engine that chips a card off your library each combat. That makes it a graveyard-fueling creature rather than a clock: the point is not the one damage in the air, it is the accumulation underneath, the top card of your library sliding into a yard you presumably want stocked for delve, flashback, reanimation, or threshold-style payoffs. Flying keeps the attacks honest, ensuring the trigger fires against most ground-based defenses without needing to punch through. It is a self-mill effect stapled to a body that survives long enough to keep milling, which is a more disciplined way to fill a graveyard than a one-shot spell: the card commits to the plan across many turns instead of front-loading it, and asks you to have somewhere for those cards to go.