It wasn't too deep on features, this was my first game I made and I just started programming =P I had 6 different things, the homing ones, the spiral, and then 4 wall ones that came from each direction. After that, they just get faster. Yeah walls are dangerous haha. I'm not sure how I'd work out that outside the boarder spawn, since technically, they all spawn outside the board (besides the spiral). Maybe a blink when something is coming from that wall? Like a little color bar, single pixel long or something?