Morelull's best moveset in Pokémon GO is Astonish and Dazzling Gleam, with 7.03 damage per second, and it can deal 88.3 damage before Morelull faints. This is true when battling in neutral weather.
All Morelull movesets ranked
Here is a complete list of Morelull movesets in Pokémon GO, ranked by their DPS and TDO. You can change the weather and the opposing Pokémon.