I added background scrolling to this game. It does lag the game a bit. I divided the task up for the enemy object to occur every 3 frames, so 2 enemy movement would be process per frame. Every frame or so, it'll lag a frame since the tiles are redrawn every 8 pixel have been scrolled. So every 48 frames, it'll have that one lag frame. Other than that, the game is stable. Occasionally the < ship get flicker in the wrong direction a brief moment.

I added the green blob enemy that follows your ships y position. I added a powerup box. Since enemies are programmed to be collided to your ship, so you have to shoot it to get that specific power up. The powerup is depending on what color it is when you break it open. Example, a gray box will grant you the missile weapon. I also made it so if you break it open with the weapon you are equipped, it'll upgrade that current weapon. Such as if I hit the gray box with the missile weapon, you'll gain a more faster and powerful version of that missile. I always love getting a more powerful weapon in shoot'em up. There's only level 2 version of the weapon. It'll revert back to 1 if you break it open with a level 2 weapon.

One thing I not sure where to go with this game. In my mind, I kinda want to be a Halley Wars type of game where you're not allowed to let any enemies get by. Also, I want to have a boss fight, so I'll have to add size option to the sprites already bloated game. And figure out what lies beyond the repeative scrolling. I'm up 11KB now. I probably origin the procedures to $D000, and the graphics $F000 to get me up to 32KB.