Please consider running the desktop Linux or Windows versions as graphically they're much better than the web version, treat the latter as a quick test to see if you're interested.
There's also gamepad and mouse/keyboard support.
Possible in-game actions:
- Go up/down and inward/outward between the rails
- Kick barrels and mines to launch them at the Boss
- Break obstructions like walls with a well timed kick
- Your shield will protect you from all damage
- Your shield will deflect Boss bullets
- Kick Boss bullets to deflect them but take some damage (if your shield is down)
- Navigate the level to replenish your health and shield