Muk

Type Tier
Poison BL
Statistics
Stat
HP
105
413
Atk
105
308
Def
75
248
SpA
65
228
SpD
100
298
Spe
50
198
Name Item

Mixed Attacking Muk

Leftovers
Moveset
~ Fire Blast
~ Explosion
~ Sludge Bomb
~ Curse / Giga Drain

Fire Blast is there for all of those Steel Pokémon that will be coming in because Sludge Bomb/Explosion won't touch them. If you ever dispose of the Steel/Rock/Poison Pokémon, you can Curse up and do as much damage as possible, then Explode. Giga Drain is for Rhydon and Golem.

Other Options

There's Rest if you like it, and if you really want to, you can use Mean Look if you think you can trap something and Explode on it.

Opinion

Muk isn't exactly a very easy Pokémon to use since many things counter him with relative ease in addition to the fact that he can be pretty predictable. However, Muk has some good stats in his favor (notably HP, Attack, and Special Defense, similar to Snorlax), which gives him more chances to switch in and try to hurt something. And if nothing else, he learns Explosion, which will undoubtedly kill something. Just watch out for Rocks/Steels/Ghosts when you're exploding!

Counters

Pretty much every physical type Pokémon is a counter to Muk. His best use is just to try and surprise something with Fire Blast or Giga Drain and then kill something with Explosion.