Liasha, Maddened Tax Collector

Creatures you control gain extort. (Whenever you cast a spell, you may pay {w/b} If you do, each opponent loses 1 life and you gain that much life.)
Pay 4 life: Detain target creature. If it's already detained, destroy it instead.
At the beginning of your upkeep, if your life total is less than your starting life total, transform Liasha