Cheapest priced copy (The List): $0.59 at Card Kingdom, near mint, their price list as of .
Thrull Parasite 
Creature — Thrull · 1/1 · Uncommon · The List · #GTC-81
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.)
{T}, Pay 2 life: Remove a counter from target nonland permanent.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.59 to $6.99 at Card Kingdom
6 rulings from Wizards of the Coast
- 24 January 2013You can't activate Thrull Parasite's last ability to stop a player from paying the cost of a spell or an ability that requires removing a counter from a permanent (such as a planeswalker's loyalty ability).
- 24 January 2013The nonland permanent you choose as the target doesn't have to have any counters on it. If it has more than one kind of counter, you'll choose one of those counters when the ability resolves.
- 12 January 2024The extort ability doesn't target any player.
- 12 January 2024The extort ability resolves before the spell that caused it to trigger. The ability resolves even if that spell is countered.
- 12 January 2024The 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.
- 12 January 2024You may pay {W/B} a maximum of one time for each extort triggered ability. You decide whether to pay when the ability resolves.