Muk

Muk is by no means a fantastic Pokemon, but it has a few unique traits that distinguish it as viable. Its large HP, Attack, and Special Defense allow it to have decent matchups versus Zapdos, Raikou, and Suicune. Furthermore, its access to Curse and ability to outpace Snorlax mean that it has the potential to hold its ground against it in a one-on-one matchup. Muk's access to Explosion makes it a decent fit on offensive teams centered around the move, and with Curse, Muk is one of the best Pokemon at forcing at least a trade, similarly to Curse + Explosion Steelix and Curse + Self-Destruct Snorlax.

However, Muk has a bad Speed tier, and its typing doesn't grant it many useful resistances. Besides Machamp without Earthquake and Heracross, it doesn't check any offensive threats well. If Muk has been worn down, many faster Pokemon are capable of revenge killing it. Muk can also have a hard time dealing with non-Steel-type Pokemon that resist Sludge Bomb and Explosion like Gengar, Tyranitar, Golem, and Rhydon. These flaws make it difficult to justify Muk's place on offensive teams over other Explosion users like Exeggutor and Gengar, which offer significantly more defensive utility and are more effective at luring Pokemon like Raikou, Snorlax, and Zapdos. However, Muk distinguishes itself by majorly threatening stall teams with its coverage, Toxic immunity, and ability to boost with Curse.