Your ship is equipped with extremely destructive weapons, but as usual the enemies are no easy targets either. Hold the Z key for a standard beam, or press the X key to clear bullets caught in your blue beam's path. Use both keys together for a special attack which causes massive damage, but use it with care as this weapon tends to overcraft and may destroy your craft altogether. An online high score submission feature is included, and you can press C to play with an alternative ship.
Sorry to bump, but there's a problem with the game.
The version available to download standalone (http://www.charliesgames.com/cactus/trash.zip) is seemingly crippled. There are no instructions at the start, and the C key and the function keys don't work.
The version included in "Cactus Arcade" works just fine though.