Correct me if I'm wrong, but Ditto, Mew, Latias, and Zorua are the only pokemon canonically shown to be able to transform into humans, right? I haven't seen all of the anime, so correct me if you know of any others, but all the other pokemon that have appeared human before like Ghastly, Ninetails, Mismagius, and Elgyem were only using illusions and mind tricks of a noticeably less tangible variety than Zorua and Zoruark's.

Honorary mentions for:
Manaphy for being able to temporarily put a pokemon mind in a human body with heart swap.
Mimikyu because it is technically possible and on brand for it to inhabit a human disguise.
Meowth and any pokemon in team rocket for being able to trick the characters if not the audience.