Jace, the Perfected Mind

The mill-planeswalker every deck wanted for the loyalty math, not the strategy behind it. Its ultimate is not really an ultimate: the -X mills for three times X, so at five loyalty it can strip fifteen cards off a single library in one activation, a Phyrexian mind-flay that treats the loyalty pool as a countdown rather than a resource to protect. Fifteen does not empty a sixty- or hundred-card deck, but it accelerates a mill clock more brutally than any single tick has a right to, and it does the work the turn the card lands. The more revealing choice is the compleat cost. Paying two life instead of blue mana drops it into play with two fewer counters, so the same card is either a durable five-loyalty threat or a rushed three-loyalty one, and the pilot decides which at the moment of casting rather than at deckbuilding. That flexibility governs the whole design: the -X scales off current loyalty, so cheating the card in with life shrinks the biggest mill it can throw the turn it arrives and turns a finisher into a lesser draw engine or a chip-damage deterrent. The +1 handing out -3/-0 rather than -3/-3 makes plain that this was never built to defend itself; it slows a single beater for a turn while the mill does the killing. Most planeswalkers reward you for ticking up. This one is built to be spent, and the compleat discount exists precisely to tempt you into arriving too small to spend big.