Say a Ditto Transformed into Litwick. Litwick used some move (let's say Hex). Next turn your Litwick (Ditto) uses Imprison. Because this seals the opponets moves, would the other Litwick have to use Struggle?
Struggle will automatically be used by a Pokémon that has no usable moves but is ordered to attack, and is not affected by any PP limitations.
Yes, a Pokemon that is unable to use any of their moves due to Imprison will use Struggle if it tries to attack.
Source