Is this what your shadow flickering issue looks like?:
I knew I'd seen it in vanilla Melee before, and I found a way to easily reproduce it. Looks like it happens whenever two textures or objects are at the same z-index (probably the same for other axis too). I remember it appearing on some really old stage hacks too, with all vanilla structures. I imagine it was caused by structures (with textures) that were in the same position on one of their axis. (Also happens when you spawn a lot of the same item into the same space, iirc)
Maybe the game normally renders shadows onto a separate object from the texture, and offsets it slightly somehow. And so in the cases above with the flicking, they're not offset as they should be. Perhaps the positional data for a shadow could be compared to the positional data of something it's known to go with. If the pair doesn't have separate positional data, maybe this is something done automatically whenever the shadows are rendered, and they're not being offset for a different reason (flag? structure order or type?).
Just some thoughts.
Z
zankyou
Achilles1515