Smeargle

Type Tier
Normal BL
Statistics
Stat
HP
55
313
Atk
20
138
Def
35
168
SpA
20
138
SpD
45
188
Spe
75
248
Name Item

Trapper + Baton Passer

Leftovers
Moveset
~ Spider Web
~ Protect
~ Disable
~ Baton Pass

If you're facing a pseudo-hazer, use the moves in order: Spider Web when they come in, Protect when they Roar/Whirlwind, Disable it, and then Baton Pass to its appropriate counter. If they switch to a Sleep Talker when you Spider Web, just Baton Pass to the counter; at 100% health, Smeargle can take any hit that's not Super Effective on it (except Megahorn from Heracross, which has an approximate 16% chance of OHKOing Smeargle—odds are still greatly in your favor).

Name Item

Stat-Up Baton Passer

Leftovers
Moveset
~ Spore
~ Belly Drum / Agility / Swords Dance
~ Recover / Encore / Super Fang
~ Baton Pass

This is the more traditional Smeargle. Spider Web isn't listed because Sleep Trapping is considered cheap in GSC by some. Put something to sleep, Belly Drum/Agility when they're helpless, and Baton Pass to your sweeper. Recover could give you another shot at doing it if it doesn't work, you could Encore a non-damaging move to maybe give you some time to Baton Pass Pass, and Super Fang is there to try and force something to Rest so you get a free turn.

Name Item

Spiker

Leftovers
Moveset
~ Spikes
~ Encore
~ Destiny Bond
~ Mirror Coat

This is a pretty good and unexpected set. Spikes is always nice, Mirror Coat is generally unexpected but will OHKO any Special Attacker if you predict correctly, Destiny Bond can take something else with you, and Encore is just a cool move in general to mess things up.

Other Options

To be honest, despite learning every move in the game except for Explosion and Selfdestruct, those three movesets covered every worthwhile move on Smeargle.

Opinion

His stats are just too crappy. If he were a little faster, he would be great, but his mediocre Speed, coupled with the fact that he can't take a hit, leaves something to be desired. He can screw a lot of teams (in particular stall teams), but a lot of it has to do with extreme prediction and extreme luck.

Counters

Any attacking move will cripple Smeargle. Paralysis also makes Smeargle pretty useless since Speed is really the only stat he needs to worry about. Switching in a Sleep Talker on Spore is a good idea since he relies on that free turn from sleep to set up his moves.