The classic shoot’em up Space Firebird has been completed as a core and added to MiSTer.
It uses the weirdest video hardware of any game I have ever seen, and this core was created in an attempt to understand the circuitry a little better.
The sprites are in 3-3-2 colour, via a lookup table (same as Galaxian and many others), but then there is a separate circuit that can pull these colours to ground via different resistors which adds 4 levels of intensity that is used when the ships appear to make them look like they are fading in.
Stars are static but a register under CPU control can vary the intensity of them a little to give the appearance of them flashing.
Incidentally, when in cocktail mode and the picture is inverted for player two, the stars stay in the same place as they did for player one. That circuit is not aware that the screen has been altered.