The Training Glitch breaks the AI in Stage 1, allowing your team of heroes to fully upgrade their starting stats for free (just beat up the CPU opponent for free and get JACKED). This makes the game almost playable.

To activate the Training Glitch, at the main menu, select "TRAINING", then press ESC and select "RESTART". This will bring you back to the title screen. Select "GAME" and the first level training CPU should not move or attack.