Press L or R to spawn an item in Yoshi's mouth. Works with shells of different colours, Goombas, Springs, P-Switches and Keys. Did not test every other sprites but I don't think anything else works properly. File includes settings at the top to select which sprite to use, timer for Yoshi's swallowing, and sounds.
Tested with: Lunar Magic 3.21, UberASMTool 1.4, SA-1 1.32, Snes9x 1.60. The fix works so it's not possible anymore to spawn a null sprite with this, so accepted. I removed a "STZ $58" which I assume was left over from testing.