Used the Fire Cannon and the Fire Lady. Abused Fire and this is as far as I got.
sadly couldn't get as much levels, but holly guackamolly, abusing fire works so well! especial with splinter and burn heal. The enemys die and shoot out fire bullets causing other enemys to burn and die causing etc etc etc and the enemys exploding in burn counts, so, you can just run around and the instant you get hit you heal!