If the attacking spaceships comes all the way down
to your spaceship you lose two lifes
Bonus lifes every 10000 points
When the ufo passes - try to hit it, when you do
you gain 1000 points and a new missile
500 points for completing each level
The attacking spaceships may have one more bullet
on the screen for each level, the game also moves faster
You may have 6 bullets on the screen at any time
(and only one missile)