Tithe Drinker

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
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.)

The List

Commander 2017

Lifelink
Extort (Whenever you cast a spell, you may pay {WB}. If you do, each opponent loses 1 life and you gain that much life.)

Dragon's Maze

Lifelink (Damage dealt by this creature also causes you to gain that much life.)
Extort (Whenever you cast a spell, you may pay {WB}. If you do, each opponent loses 1 life and you gain that much life.)

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.