>>58242043
>In the anime it was implied that was a problem with that particular Ditto, and IIRC at the end of the episode it was able to overcome it and transform entirely, including it's face.
Ironically, that specific Ditto not being able to transform its face ended up being so iconic that it they just canonized it as a thing Dittos usually do. It's appeared in basically EVERY piece of Pokemon media that's included the thing.

Even the mainline games had a Clefairy in the gen 4 slot machine that would occasionally be replaced by a Ditto with Dittoface.