Board Thread:Pokemon Arena X - In-game News/@comment-5398529-20150124214139/@comment-5871369-20150204185629

Another idea is like you have to get items to unlock the pokemon or trade a pokemon to unlock evolutions or other pokemon. Could be similair to the quest system mentioned by Midget or like a secret unlockable when you have the pokemon or items for the trade.

You would of course lose what you had but instead gain a pokemon.