Remap game buttons and use the skill level select for game mode.
From original user guide:
- Skill Level "1" - Alien fighters attack one at a time.
- Skill Level "2" - Alien fighters attack one at a time but combat speed is faster.
- Skill Level "3" - Alien fighters attack two at a time.
- Skill Level "4" - Alien fighters attack two at a time but combat speed is faster.
When game is switched on, skill level is automatically set to Level "1" and "1" is displayed at top of Game Display.