Treasury Thrull

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.)
Whenever Treasury Thrull attacks, you may return target artifact, creature, or enchantment card from your graveyard to your hand.

The List

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Extort (Whenever you cast a spell, you may pay {WB}. If you do, each opponent loses 1 life and you gain that much life.)
Whenever Treasury Thrull attacks, you may return target artifact, creature, or enchantment card from your graveyard to your hand.

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Commander 2015

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The amount of life you gain from extort is based on the total amount of life lost, not necessarily the number of opponents you have. For example, if your opponent's life total can't change (perhaps because that player controls Platinum Emperion), you won't gain any life.

The extort ability doesn't target any player.

The extort ability resolves before the spell that caused it to trigger. The ability resolves even if that spell is countered.

You may pay {W/B} a maximum of one time for each extort triggered ability. You decide whether to pay when the ability resolves.