oh wow... did not know you could do that with the Analogue Pocket?! So that was a SNES core running a SGB core too? Mind blowing!
The multi-player part of this is probably my worst work...(!) It's very clunky and not optimised at all, which is why they are 'stone columns' to give the impression of being slow(!!!)
I'd love to share a multi player project when I can get the part optimised, showing 2 player, and also 4. The Jam version polls the joypad ID values and works out which pad is pressing what. Then every 0.5 seconds it updates the 'stone columns' to move a tile. It's messy, to say the least!!
But I will make a note to seek some help to better optimise the controlling to get an example project out there.
You should check out Bobby Volley GB on itch... they have a 2 player SGB game for GB that plays very smoothly 👌🏻 . No project files sadly.