This Ability effect may be in need of research. Reason:If a Pokémon with Imposter is the wild Pokémon of a Raid Battle (e.g. Max Raid Battle), who will Imposter copy? You can discuss this on the talk page.
Imposter will not activate if the opponent is transformed, is disguised with Illusion, is behind a substitute, or is a Starmobile. Imposter only activates when the Pokémon with the Ability is sent out; if it fails to transform into an opponent, it will not activate unless the Pokémon with Imposter is withdrawn and sent out again. Imposter will also not activate when obtained during battle.
In Double Battles, Triple Battles, and Battle Royals, Imposter will target the opponent in the position directly opposite it. If there is no opponent directly opposite it, it will not transform. In Horde Encounters, Imposter will copy the opponent in the right-most position. If the opponent of a Tera Raid Battle has Imposter, it will transform into the host's Pokémon.