Snes shadows

I've been looking at SNES games, and I see a lot of games that use a checkerboard dither (black vs transparent), to do shadows that blend into the background. Urban Strike is an example (and hundreds of sport games). This looks kind of ugly to me. I'd prefer a solid dark for a shadow.

Then I saw a few games that had a half transparent effect for shadows...
-Power Moves
-Street Combat
-TKO Boxing (best example)

Does anyone know how these shadow effects are done (that blend with the BG)?

Also interesting, is NBA All-Star Challenge, which seems to be blending players 'reflection' with the floor. I have a feeling this is the same effect.

It varies per game, and I'm not willing to RE every single game. Most commonly it's accomplished with one of several approaches, or possibly a combination:

- Screen addition/subtraction: registers $2130-2131, $212C-212D
- Colour constant addition/subtraction: $2130-2132
- Colour windows (has my vote): registers $212E-212F, $2125-212B, $2130-2132

Otherwise it's done in software and appropriate tiles created/manipulated (likely alongside use of the above). I played around with screen addition/subtraction in my old "iNFiNiTY" demo as part of my old SNES docs.