Sometimes it’s difficult to know if the emulation of a game is correct without studying reference videos, and sometimes those reference videos don’t surface until much later.
That was the case with the FACE shooter Nostradamus, which has a number of video effects we didn’t know were missing until they were highlighted by somebody watching a 1CC (1 Credit Clear) of the game recorded from a PCB.
There were a number of effects, including a sprite masking effect and a shadow flicker effect missing, as well as the arms of the final boss (this one we did actually suspect was a bug for a long time, the PCB evidence provided confirmation)
I’ve uploaded a recording of the game after making several fixes to YouTube (the video has cheats enabled, it’s not meant to be a gameplay video) You’ll probably want to make sure you’re watching a 60fps version.
Here are some links to specific parts of the video
Stage 6 Boss appearing – This is a masking / stencil effect created by putting a sprite behind the background layer causing it to cut holes in other sprites without being directly visible
Stage 7 Boss appearing – This flickering shadow is not actually a sprite and is done by using the tilemap enable register, turning it on and off every few frames, previously the tilemaps were alwyas enabled and the shadow was displayed as solid.
Final Boss arms – The arms are priority 0 sprites, and due to the way we cleared the priority buffer to 0 they were never being displayed.