Raven Guild Master

Mill as a clock you can hide. Most library-attrition cards grind in increments and ask the opponent to die slowly; this one connects once and exiles ten cards off the top, then keeps a flimsy 1/1 body in combat to do it again. The face-down disguise is what makes that math threatening: an opponent staring at an unflipped 2/2 has no way to know they are looking at the difference between a no-trade and ten cards gone, and the morph cost can be paid mid-combat after blocks are declared, so the trick lands at the worst possible moment for the defender. The exile clause matters as much as the number. A player who loses ten cards to the graveyard can still rebuy them with recursion; ten cards to exile are simply gone, which turns this into a genuine deck-out threat rather than a graveyard-fueling nuisance. The 1/1 frame is the honest cost: face up it dies to almost anything, so it lives only as long as nobody respects the morph, which is exactly the window the card is built to exploit.