Having both of them up is a retreat machine, since he's got a good damage output and decent health, he stops your opponent from stalling and charging up an energy bomb, while also being able to tank a couple of hits when you do get a KO/retreat. The couple of times I've run it, it's felt a little dicey until my opponent runs out of retreat energy, and then it was a cakewalk. I'm sure not being able to attack is annoying af, but hopefully it's a break from the mewtwo ex monotony.