Chatter is the only move that cannot be sketched.
As such, Sketch and Chatter are the only TRULY signature moves (due to all the others being able to be metronomed or sketched)
Are you sure? When I trained a Smeargle once I tried to Scetch Transform. I never cleared it. Was I just unlucky?
Btw. About Smeargle, did anyone know that it is based at the real life dog, Smear Beagle? That dog was a kind of artist i heard, a painter.
I heard it from a Fact one time in the past. Mabye I have been tricked...
I know more:
Mr.Mime is based at a phatomimer called Marcel. Hence its name in FR/LG and R/B/Y.
Hitmonchan and Hitmonlee is based at Jackie Chan and Bruce Lee.
... and I already told you about Smeargle, right?
It is probably more pokemon of thet kind?