Let's talk about the controls. In Mystical Ninja Starring Goemon, I actually had to use the instruction manual to figure out how some parts of the controls work. Here's a simple list that can be useful for speedruns:
Swap Characters: C-Down
Zoom in Camera: R + C-Up
Zoom out Camera: R + C-Down
Rotate Camera: R + C-Left / Right (Turn left and right)
Laser Mouth: C-Up, C-Right, C-Down, C-Left, Z-Trigger
Super Punch: C-Up, C-Down, C-Up, A
In the Impact Bonus Stage you hold the Control Stick Up (Impact Bonus Stage fastest movement).