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I mean, its typing is solid, with Dark completely negating any Psychic troubles, and Poison lessens Fighting's impact.
However, the stats on this bitch are horrid. It has only 67 Def, 61 SpD, and is saved partially by 103 HP. The attacks range from 93 Atk to 71 SpA, and it has a decent speed of 84.
Raising both defenses to 87 and 81, Def and SpD respectively, will give it enough bulk to handle a few hits in maybe RU or the tier above. Raising the Attack stat to at least 105 will allow it to push around the many fairies polluting the lower tiers, and its speed could be 90 or so without too many problems. The Special attack stat would need to be at least 94 to utilize Sludge Bomb, Shadow Ball, and a new Sludge Wave, to its reasonable best.
Speaking of new moves, it could benefit from Psyshock, with potential reasoning that the stench from it was weaponized to mind-breaking effectiveness.