Adun's Quick Guide to Pangya Special Shots
First of all, you don't need a Strength Potion. That's a mistake I made from the start. :B
A prerequisite to performing a special shot is a Power Shot (Press Alt with at least 1 Power Shot in stock).
Begin your shot and apply at least 80% power. When the slider starts coming back to 0 and after it passes 50% power, you can then input button commands to activate a special shot.
Tomahawk: Press up + down.
Cobra: Press right + up.
Spike: Press right + down.
If you have applied a spin to the ball, you can make it a Power Spin or Power Curve. However, you have to hit a Pangya if you want to have a Power Spin/Curve.
Power Spin Forward: Apply forward spin. Press and hold up. Hit a Pangya.
Power Spin Back: Apply back spin. Press and hold down. Hit a Pangya.
Power Curve Left: Apply spin to the left. Press and hold left. Hit a Pangya.
Power Curve Right: Apply spin to the right. Press and hold right. Hit a Pangya.
These can be combined in many ways like this...
Power Spin Forward + Tomahawk: Activate Power Shot (Alt key). Apply forward spin (Ctrl+Up). Begin the shot. Input up + down + hold up. Hit a Pangya.
These all take lots of practice but you can do all sorts of things with them once you master the combinations.