Hollow Marowak
Ground Trainer
I think Iris is currently sort of "in-training" for the 8th gym leader. That would explain why exaclty she is on the journey currently, besides raising Axew. I think when they get to the 8th city(forgot name) Iris should battle Drayden for the title of Gym Leader, lose and then rechallange him and win. Then she becomes the new 8th Gym Leader and Ash fights her for the badge. That'd be a good way to showcase both Iris and Drayden and give them good gym battles.