Tip: Layer 3 backgrounds and tides disappear when you hit a message box, so plan your level around that. For example, you can add a sublevel without layer 3 at the start/midpoint, and include your message there.
This is a pack of 2 sprites, the Splitting Giant Goomba and Splitting Mega Goomba that are loosely inspired by the sprites of the same name in NSMB Wii as well as the Marchin' Milde boss in Yoshi's Island. The Mega Goomba must be spin jumped a configurable number of hits to split into 2 Giant Goomba, which can be hit normally to turn into 2 regular sized Goombas. Look at the README for further instructions.
(Rykon-V73) Small update: Added the 2 .json files for both the giant goomba and mega goomba sprites and added ExGFXAD.bin and ExGFXB0 in the archive. I feel those are better, but you decide.
This is nice and all, but I'd recommend some sort of extra bit or config (or if need be, an extra .asm file) for the Splitting Mega Goomba so that it can use regular stomps to split. This would mean that hacks that remove the spin jump could use it. Also because NSMBWii had the spin jump and didn't require you to use it on the biggest Goombas, so that would make hackers editing this to split into two Hefty Goombas and then two Goombas possible and more accurate.