One technique that is particularly helpful against most of the Boss stages is to use the Slide attack. Use Slow + Slide repeatedly. This does a decent amount of damage in a short time. You can hit the Boss four to eight times if you are fast enough, while the Slow adds more damage to each attack.
Finish flip in Normal mode
When your VFX bar's first container is half full, use Slow Motion (hold L) and double jump. If timed correctly, you will do half the flip in Hero mode and half in Normal mode. If you want it to look even better, use Slow Motion and Double Jump just as Joe transforms into Hero mode. If timed correctly you will do your flip with the transformation glow around you.
V-Rated difficulty
The V-rated difficulty makes the game harder by raising the price of moves, making the VFX Gauge run out faster, and increasing the power, health, and speed of enemies.
V-Rated mode
Successfully complete Single Player mode on the Adults difficulty setting to unlock the V-Rated difficulty setting.