518 Musharna

Charge Beam lacks STAB and isn't particularly strong, but is chosen for its faster energy generation, letting Musharna access its charge move sooner. Zen Headbutt is a very poor move despite benefiting from STAB. 

Psyshock costs the least amount of energy and benefits from STAB, becoming Musharna's main charge move. Future Sight has a significantly higher energy cost and is therefore less preferable. Dazzling Gleam demands a large amount of energy, but provides additional coverage, notably against Musharna's weakness to Dark-type Pokemon.

At first glance, Musharna's high STA stat would suggest it would perform well in PvP thanks to respectable bulk. Unfortunately Musharna is best slept on, as its moveset options are quite poor and result in terrible performance against the overall meta. Charge Beam lacks both damage output and energy generation compared to many other fast moves, and while Psyshock isn't terrible, its stats are above average at best. This is notable enough for Musharna to lose matchups that it would be expected to win, such as versus Venusaur due to Charge Beam's slower energy gains and resisted damage, and Frenzy Plant out-damaging a Super Effective Psyshock, or even against Shadow Machamp if the Fighting-type lands one successful shield bait in a 2-shield scenario. With multiple other Psychic-types in the meta, it's best if Musharna does what it does best: sleeping. 

Musharna's moveset problems are as notable in Ultra League as they are in Great League. Wins against Fighting-types are to be expected in this league, but unfortunately that seems to be Musharna's only niche. Even in Ultra League Musharana can't beat Venusaur in a fair fight, despite threatening a Super Effective Psyshock. Meta Psychic-types like Cresselia, Armored Mewtwo, and Bronzong also tend to out-perform Musharna in this league, making it hard to justify Musharna's use. 

Musharna lacks stats to perform well in Master League.