When your VFX bar's first container is half full, time it so that when you do a Slow Motion (hold L) and double jump, you do half the flip in Hero mode and half in Normal mode. If you want it to look even cooler, use Slow Motion and Double Jump just as Joe transforms into Hero mode so that you do your flip with the transformation glow around you.
When fighting Bosses, use the Slide attack. Use Slow + Slide repeatedly. This will inflict a large 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.