Thrull Parasite

• WWizards of the Coast2013-01-24
  Official Ruling
  You 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).
• WWizards of the Coast2013-01-24
  Official Ruling
  The 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.
• WWizards of the Coast2024-01-12
  Official Ruling
  The extort ability doesn't target any player.
• WWizards of the Coast2024-01-12
  Official Ruling
  The extort ability resolves before the spell that caused it to trigger. The ability resolves even if that spell is countered.
• WWizards of the Coast2024-01-12
  Official Ruling
  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.
• WWizards of the Coast2024-01-12
  Official Ruling
  You may pay a maximum of one time for each extort triggered ability. You decide whether to pay when the ability resolves.

Rulings via Scryfall