. . . you won't just be gone, you'll be forgotten . . .

Aetherize

Return all attacking creatures to their owner's hand.

Secret Lair Drop

"You can come back once you've learned some manners—and figured out how to reconstitute your physical forms."

Bloomburrow Commander

The List

Ravnica Remastered

The Lost Caverns of Ixalan Commander

An "attacking creature" is one that has been declared as an attacker this combat, or one that was put onto the battlefield attacking this combat. Unless that creature leaves combat, it continues to be an attacking creature through the end of combat step, even if the player it was attacking has left the game, or the planeswalker it was attacking has left combat. There's no such thing as an attacking creature outside of the combat phase.