Ban.
Why should we ban Musharna? It's great balanced stats in combination with a very wide movepool makes it very useful in the PU tier, maybe a bit too useful. There are quite less Pokemon that can beat it, as PU has a low amount Dark- and- Ghost-types, that are able to defeat Musharna, leaving it basically with only weak Bug-types that can damage it with super effective STABs, where Musharna can tank a hit from and easily defeat them with Psychic.
You aren't able to do a lot of damage by status, as it has access to cleric support in Heal Bell, but also stops set-up sweepers by paralyzing them with Thunder Wave, and switch out after, or just KO it as it has a high base Special Attack and two good STABs in Psychic and Psyshock.
Coming back to the wide movepool part I mentioned in the beginning, Musharna can succesfully fill in different roles in the PU metagame, for example a bulky cleric set with Heal Bell, a Trick Room setter or an All-Out Offensive set, that all most likely provide success.
1. Bulky Cleric Set
Musharna has great bulk on the overall (116/85/95) meaning that it is almost guaranteed to pull of a Heal Bell, that is excellent for teammates that are crippled by status, such as Tauros, but also helps Musharna itself, as it prevents it from being crippled by Toxic damage. Moonlight allows it to recover a good amount of HP, especially when used on a sun team. After it has recovered, it can take some hits and beat offensive Pokemon with Psychic, or just inflict Status on them.
2. Trick Room
As Musharna has very low Speed, not only it provides itself by outspeeding most Pokemon in the tier after except for Gigalith and Avalugg, but also helps slower Pokemon, such as Marowak functioning way better by KOing Pokemon without fearing to take damage from some.
3. All-Out Offensive
Musharna has also a good wide offensive movepool (Psychic/Psyshock, Dazzling Gleam, Shadow Ball) that allows it to do its job well as a Special Attacker, because it has a great Special Attack stat that disallows opponents to switch-in very easily and like mentioned earlier, a wide movepool. Trick Room support is especially useful on this set as Musharna is very slow, and boosts its longevity as it has to take one less hit. It can recover from being attacked, and continuing attacking further, and beats several Fighting- and Poison-types in the tier, but also 2HKOes bulky Dragon-type Pokemon in the tier such as Fraxure with Dazzling Gleam.
Aside from these good points, you do not really need two team slots to take care of Musharna, as a bulky setup sweeper, preferably those with recovery, can get rid of Musharna. Also, Pokemon that can Trick Musharna when using a tank set, allow it to limitedly use a single, damaging attack (assuming the tank set is used which I think is the best for it)