My entry as a check to this Musharna set is
Substitute + Disable Haunter.
Haunter @ Black Sludge
Ability: Levitate
EVs: 4 Def / 252 SpA / 252 Spe
Timid Nature
- Substitute
- Disable
- Shadow Ball
- Sludge Bomb
This Haunter set is a check to Musharna, but it isn't a counter, as it doesn't want to take Psychic or Thunder Wave immediately. However, it can come in on an obvious Moonlight, or of course if something has fainted. Basically, the set works very simply. Typically when Musharna is in a matchup with Haunter, it'll switch out, at which point a Subsitute will be gained and Haunter will be able to do work to the opponent's team. If Musharna does stay in (due it having enough health to not be KOed by Shadow Ball, which is around >65%, and not wanting to face a Haunter behind a Substitute), then it will either use Psychic or Thunder Wave. If it uses Thunder Wave as Haunter uses Substitute, Haunter can 2HKO it with Shadow Ball while it is forced to break the Substitute with Psychic or switch out, Haunter winning the matchup. If it uses Psychic as Haunter uses Substitute, Haunter will then use Disable to prevent Psychic from being used again, then it will Substitute again. There is a small risk in Musharna Thunder Waving as Haunter uses Disable but that would require the Musharna user to know that it is a SubDisable set and not something like Sub + Will-o-Wisp + Taunt and risk losing momentum if he mispredicts, making it a very unlikely scenario. Typically, using Substitute on the Psychic twice is a good plan since it usually allows you to discover whether the opponent thinks you have Disable or not; it is very unlikely it will Thunder Wave on the third turn of the matchup.