429 Mismagius

Hex is generally recommended for its superior energy gains along with benefiting from STAB. Sucker Punch lacks STAB and as a result the damage difference between the two fast moves is minimal, but is a step down in energy generation. 

Shadow Ball is powerful with STAB and efficient in Damage Per Energy (DPE), though it has a moderately expensive energy cost. Dark Pulse costs slightly less energy, and is the cheapest charge move option available. Dazzling Gleam provides useful coverage, especially against Dark-type Pokemon, but its high energy cost is unappealing. 

Mismagius is a pure Ghost Pokemon, which is rather unique as most Ghost-types in the meta have secondary typings. A high ATK stat consequently results in poor bulk due to the CP cap of this league, making Mismagius rather fragile and more of a risky pick. A cumbersome moveset that lists Dark Pulse as the cheapest charge move option is rather slow compared to the rest of the meta, and the lack of more accessible coverage options puts Mismagius behind other Ghost-types for its role. 

Challenging Giratina is a tall order in Ultra League, and Mismagius doesn't pose any real threat with its fragility and slow moveset. In formats that exclude powerful legendary Pokemon like Premier Cup, Mismagius doesn't perform too well either due to the same reasons. Consider other Pokemon instead. 

Mismagius doesn't have sufficient stats for Master League.