Invincibility

Using the special move (Star powerup) as bubbles activates invincibility.
If you press punch, it cancels the animation, then switch to another girl and you will have permanent invincibility.
The other girls will be in a glitch state that can still shoot, however if you punch with them, they will be restored, and able to collect power ups and such while still being invincible.

Brienie

The Powerpuff Girls: Mojo Jojo A-Go-Go