Just so, what's super effective against Uxie?
Uxie is a psychic type Pokémon. psychic type pokémons are strong against fighting, poison, ghost pokémons but weak against bug, shadow pokémons.
Secondly, how many trainers does it take to beat Uxie? As a bit of a tankier Pokémon than Azelf, Uxie is a difficult but possible trio. Going in with four or more strong trainers will be the best bet if you can't guarantee the top counters.
Subsequently, one may also ask, how do you fight Uxie?
Max out your damage with Ghost-type and Dark-type Pokémon.
Uxie, Mesprit, and Azelf are all weak against the same three types: Bug, Ghost, and Dark. Pokémon like Gengar, Origin Forme Giratina, and Chandelure will dish out damage the fastest, so use them first if you want to do damage as quickly as possible.
Can Uxie be DUOD?
Uxie has a stat composition of 156 Attack, 270 Defense, and 181 Stamina leading to a Max CP of 2524. It appears that Uxie cannot be duoed, even with Fog weather boost and friendship bonuses.