They have levels and stats now??? I clearly missed something LOL How does this work? How do you level them up if we can??

its part of a minion battling system that is incomplete. You can level them up by battling with them. Click on any minion with stats and it will take you into battle. If you win you get more experience, but even if you lose you get a bit. It levels up automatically as you battle.

If you remove them from the minion zoo, all leveling disappears and you have to start over.

Oh wow, thanks for letting me know! That's pretty neat lol