I just noticed with the new challenger wave that a pet I got from the adoption center named Baghdad has -33,811 EXP when I went to upgrade a different pet. Using him to fight another challenger slowly shaves off the amount. Is there a reason for him to have a negative exp amount?

That happens when you accidentally spend your EXP multiple times, usually during lag. It’s completely harmless, but you have to earn back the extra EXP that was spent until the number becomes positive again.

ahh so someone donated that pet to the adoption center instead of earning the exp back gotcha