I played a random battle, and the cherrim didn't transform during sun. It made me sad because cherrim sunshine is my favorite pokemon..
for rating the cherrim, im certain speed will be needed, but flower gift increases your atk and spdef in sun (if it works here(or if it even works in singles?)) so i think hasty would be a good nature? or naive, since spdef is getting increased anyways? i dont know any physical attacks for cherrim though..since it will just use solar beam and weather ball, maybe timid or modest this is up to you
