sega genesis dev here. they might be CRAM dots from changing a 16-colour palette in the TV overscan region. basically as the TV draws the picture, they switch out a palette. this trick gets you more colours at the tradeoff of only being able to use 64 specific ones per horizontal scanline.
basically there was a bug in the sega genesis VDP, where every time you wrote a palette to the Colour RAM, or CRAM, the colour would appear onscreen as a dot. but normally you don't see this, because developers would carefully time palette updates to be in the TV's unseen overscan region.
here is my own game, Stinkead and the Seven Deadly Sins. at 0:27 look to the left of the dialogue box. to get more colours to display the "A" button, i swap out 16 colours over 8 lines at the top of the box. note the dots. i put the originals back after the button is drawn.
I think it's palette data or something similar. The FMVs for the Puggsy demo on the same disc do the same thing. It's definitely way off in what would normally be a non-visible bit of the screen.
I'm playing a PAL disc on an NTSC system, and I'm not sure if this is how it'd have looked like on a real PAL system. (Or if the NTSC version of Puggsy on an NTSC system looks like this.)
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here is my own game, Stinkead and the Seven Deadly Sins. at 0:27 look to the left of the dialogue box. to get more colours to display the "A" button, i swap out 16 colours over 8 lines at the top of the box. note the dots. i put the originals back after the button is drawn.