Well, now, since nobody is answering this, I might as well do so.
Ditto should have the move Transform in all main games. In certain side games (like Rumble), Ditto can only have Struggle. If Ditto has it's Hidden Ability Impostor, Ditto will transform instantly the turn it was sent out. If Ditto has any move other than Transform in the main games, it is hacked or has been subjected to this glitch:
In Generation II, if a Pokémon uses Sketch while transformed, it will permanently learn the Sketched move.
However, odds are that they fixed it in VGC Gen 2 games (as they did with some other things) and is extremely hard to "legitimately" obtain (if you count glitch abuse as legitimate). Hope I helped.
Source, and Source