Rainbow Karp was cursed by Evil Mew after he splashed water on Evil Mew. So now he's cursed.

Rainbow Karp is a fairy water type thanks for his curse, and he also knows all fairy moves and Draco meteor.

However he can't evolve because his curse prevents him from doing that. Which is the downside.

Rainbow Karp can also shoot magic lasers that cause things to explode more than in a Michael Bay movie.

His scales are also impervious to electricity and grass and poison. And cause dragons to melt into a pool of acid if they touch them.