This one is cheating slightly, as the gorilla has already appeared on the show, but theres plenty of reason to believe therell be more monkey business in season 2. After a couple of teasing glimpses throughout the show, the primate got its own episode, Grodd Lives, towards the end of the first season and didnt fail to disappoint. It looked very good considering the shows likely budget, and with telepathic abilities, extremely high intelligence and super-gorilla strength is more than a match for Barry. Hes only defeated by being hit by a train, but after that we see him climbing a building and getting stronger. Couple that with the fact he is one of the major Flash villains, and it seems almost certain hell return.