My my aren't we full of questions?

Anyways, welcome to the forums!
Well they aren't hidden stages but, in episode 1..:
Forest > Caves (Talk to the principal after beating the Dragon) > Mines (Talk to principal after beating De Ro Le) > Ruins (Talk to principal after beating Vol Opt)
Episode 2 line has these stages..:
VR Temple > VR Spaceship (Talk to the lab cheif after beating Barba Ray) > Centeral Control Area (Talk to the lab chief after beating Gol Dragon) > Seabed (Talk to lab cheif after beating Gal Gryphon)
Hardest Boss on Episode 1 is Dark Falz, most annoying one is De Ro Le

Hardest Boss on Episode 2 is Olga Flow, most annoying one is Barba Ray
Raising your mag is up to you to figure, that's a rule about them, if you pay attention to its stats every once in a while, you'll catch on.