I mean. Johnny is basically forced to be defensive in this fight. While he's very evasive/elusive, and he's very tanky on top of that (Toon Force, Elasticity, and Immense Pain Tolerance), this will, at best, delay the inevitable. Johnny really can't do anything offensive to Mash.
Like, Johnny can probably hit Mash with his Hurricane Hands (considering that the attack is city-sized), but that's probably it.