Board Thread:Site Discussions/@comment-25165258-20141222070847/@comment-5008588-20141227070910

Pokemon revert to level 50 in battle, it doesn't matter what level they were at before. Stats go up and down depending on the original level too. it doesn't matter.

However, we do suggest that you beat the game you plan on using. So you have a much larger range of using Pokemon and have some who are more battle ready.