Just reminiscing about graphical breakthroughs in games. I remember sitting at a friend's house playing Bug Byte's Spectres, a PacMan clone, on the 16K Spectrum circa '82, and my mate's amazement at the ghosts being, like, properly "see through" (aka XORed over each other!) 
It was a great technique, thank the gods for a relocatable stack! I remember fighting with something similar and the strange layout of the speccy screen, it was all fun and games until I needed to adjust the Modulo for partially clipped sprites at the screen edges, good times 