While resolving Perforating Artist's last ability, your opponent chooses a card to be discarded without revealing it, chooses a nonland permanent to be sacrificed, or chooses to do neither. Then that player discards that card, sacrifices that permanent, or loses 3 life. Your opponent can always choose to lose 3 life, even if they have cards to discard or nonland permanents to sacrifice.
Some raid abilities trigger at the beginning of your end step. These abilities trigger if you attacked with a creature that turn, even if the permanent with that raid ability wasn't on the battlefield when you attacked.
In a Two-Headed Giant game, Perforating Artist's last ability causes both opponents to sacrifice a nonland permanent, discard a card, or lose 3 life.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Arif Wijaya
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Raid abilities evaluate the entire turn to see if you attacked with a creature. That creature doesn't have to still be on the battlefield. Similarly, the player, planeswalker, or battle it attacked doesn't have to still be in the game or on the battlefield.
Raid abilities care only that you attacked with a creature. It doesn't matter how many creatures you attacked with or which player, planeswalker, or battle those creatures attacked.
In a multiplayer game, each opponent in turn order makes their choice once, then all of the actions occur simultaneously. Opponents will know choices made by earlier opponents when making their choices, although a card chosen to be discarded this way isn't revealed until it's discarded.
