I love Smeargle. It was the first shiny I ever caught in the Artisan Cave back in Emerald. I transferred him to Ruby and taught him transform and he would transform into the shiny version of any pokemon (in gen 3). After him, i have caught several more shinies, but he was my first <3 I wish i still had him today, but i lost my pokemon Diamond.
Anyway, he can be extremely good in the right set up. I use him for shell smash passing.