Pyukumuku's best moveset in Pokémon GO is Counter and Mirror Coat, with 5.44 damage per second, and it can deal 145.3 damage before Pyukumuku faints. This is true when battling in neutral weather.
All Pyukumuku movesets ranked
Here is a complete list of Pyukumuku movesets in Pokémon GO, ranked by their DPS and TDO. You can change the weather and the opposing Pokémon.