Using Bombs, each Bomb has a specific effect.
1) Fire: Aliens will burn.
2) Bomb: Aliens will explode.
3) Sword: Aliens will be cut.
4) Freeze: Aliens will be frozen.
Harder mode: If you stay at as low health as possible, the difficulty will be harder. And if you reach the time out, a powerful Alien will appear.
Good Ending: Your cockpit should not be destroyed in last stage.