I've been messing about with Assist Liepard, and I believe I may have found a bug.
As demonstrated in this battle-
http://replay.pokemonshowdown.com/rubeta-112323251 - Liepard can only call Sky Drop with Assist, even with other moves that can be called by Assist on the team (namely, Fly and Shadow Force). Out of curiousity, I replaced Sky Drop with Mimic on Smeargle, with the result that Assist failed when used -
http://replay.pokemonshowdown.com/rubeta-112319662 . Is this an intended behaviour? (The team I used can be found here
http://pastebin.com/WG4H4gzi )
Fly, Shadow Force and Mimic are all moves that cannot be called by Assist.
The list of unassistable moves is: assist, belch, bestow, bounce, chatter, circlethrow, copycat, counter, covet, destinybond, detect, dig, dive, dragontail, endure, feint, fly, focuspunch, followme, helpinghand, mefirst, metronome, mimic, mirrorcoat, mirrormove, naturepower, phantomforce, protect, ragepowder, roar, shadowforce, sketch, sleeptalk, snatch, spikyshield, struggle, switcheroo, thief, transform, trick, whirlwind