Yeah, Smeargle can learn almost any move, but I know it can't learn counter, cause counter always gos 2nd. Here's one awesome trick I found on Gamefaqs that has to do with smeargle and sketch, I tried it and it works!
"Mewtation
Contributed by: Jason322
Further research: Jolt135 and Donald
The discovery of this on Rememberance Day (11/11) sent shockwaves through the
entire Pokemon community.
It's simple in theory. Take a Pokemon with Transform, and face off in a trainer
battle against a Sketching Smeargle. Transform into Smeargle, defeat Smearg, and
then wait until the next Pokemon uses a move that you want. Sketch it, then beat
the second Pokemon. After the fight, the move you Sketched should replace
Transform. To get Transform back, simply run the Pokemon through Pokemon Stadium
2's Move Returner. Repeat until you have a full moveset.
What makes this so damaging? Well, it gives Ditto 246 moves to choose from (yay),
and Mew 248. Yes, 248. With its stats? God help us all.
And it gets worse, ladies and gentlemen... On January 12, 2003, I discovered
that this same trick works if you Metronome a Transform. That means there's about
seventy Pokemon by my count (possibly more) that have the potential for 246 moves."