I have a hm psyduck and I think that a corphish would be a better Pokemon to use but I don't know if I should release my psyduck or not and although I don't think there are any negative effects (apart from losing the poke ball) I'm not sure. Most likely it's ok to release a Pokemon but I want to check before I release psyduck.
Not much negative effects is there.But you must keep this in mind.
1) You will lose your pokeball (or any type of pokeball)
2) It will waste your poke money for the ball.
3) You lose your Pokemon forever .
Hoped I helped
Beside the lost Pokeball no there is no negative effect of releasing a Pokemon.
Releasing a Pokemon has no additional effect, apart from losing 200 Pokemoney, at the very least.
However, I dont usually release my Pokemon in case an in-game character wants to trade something for it.