When the Muk's moveset is a combination of a poison-type move and a dark-type move, Golem is one of the best Pokemon to beat Muk. While the Muk's poison-type fast move is not very effective against the ground-type Pokemon, Golem's ground-type moves can damage Muk effectively. Note that Golem cannot decrease the damage of Dark Pulse.
Golem can learn ground type moves, Mud Shot and Earthquake, for fast move and charge move.
The optimal moveset for Muk as an attacker is considered the combination of Poison Jab and Gunk Shot, and that for Muk as a defender is Acid and Sludge Wave. Therefore, a player may see the Muk with one of these two movesets more often than that with other movesets.
In case the moves Muk use are all poison-type, Alakazam is one of the most powerful Pokemon to fight against it. While decreasing the damage of poison-type moves, Alakazam can attack Muk with psychic-type moves which Muk is weak to.
The combination of Psycho Cut and Psychic is the best moveset for Alakzam to beat Muk. Psycho Cut is better than Confusion based on DPS and EPS and considered as one of the most powerful fast move.