Tasha, the Witch Queen

The triggered ability keys on an unusual clause: it fires on spells you cast that you don't own, which means the payoff isn't your own deck but your opponents' graveyards. That framing turns the two loyalty abilities into a two-part heist. The +1 doesn't just cantrip; it deposits opponents' instants and sorceries into exile with page counters, building a reserve of stolen material that grows every turn without touching your own cards. The −3 then spends that reserve, casting the flagged spells from exile for free. Both halves care about the same resource: the page counters are the ledger, the −3 is the withdrawal, and the Demon-token trigger fires on every one of those free casts because a spell cast off a page counter is definitionally not one you own. Most graveyard-theft cards steal a single card once; this one converts an entire game's worth of opponent card advantage into a renewable stream, and taxes them for the crime by leaving fewer answers in their bins. As a commander, that identity sharpens: the whole point is to weaponize what the table throws away, and the more removal and counterspells your opponents burn, the deeper Tasha's library of borrowed pages runs.