POP! 8-Bit: Space Invaders - Medium Invader (Yellow Gamestop Exclusive) #33
The increasing pace of Space Invaders was a very early example of "that's not a bug, that's a feature." All Space Invaders were intended to move as quickly as the last one, but the hardware that was operating the game couldn't hold up. It compensated by slowing down the invaders, gradually speeding them up as there were fewer on screen.