This code uploads different 8x8 tiles on layer 3 depending if all Yoshi coins have been collected in the level Mario is standing on or not, or if there are none to be collected at all.
Which tiles to use, their properties and position are highly customizable. See the .asm file for details.
It is advised to use this in conjunction with the SRAM/BWRAM Plus patch in order to save the player's progress made in collecting Yoshi coins.
Edits & updates:
- now the patch is very user-friendly (thanks HuflungDu)