Bug: All of my creatures fainted and the game told me to select one to fight with, for a second I thought it was mocking me but it was probably unintentional
Edit: Happened a 2nd time (on the same trainer lol) and if I had to guess a reason why, it'd be I had blobble as the last creature in my part both times, since blobble comes in 3s in your storage and if you select one to join your party, all of them do, it could be the game thinking that I still have 2 more blobbles in my party, though thats just a guess