In one of my Reborn runs I used sandbox mode to give me 6 Pokemon to use for the entire game.
Marowak
Scizor
Gliscor
Chesnaught
Aggron
Clawitzer
I pretty much did every gym with those 6. I had to switch one out for Amaria, but that was because she kept steamrolling me. The team isn't super balanced type wise, but they get the job done.