This patch allows you to... well, play as Yoshi in certain levels (that you can specify). Levels where this function is disabled will play completely normally.
Any other information should be covered in the ASM file itself.
Update: Now handles extended sprite contact properly. (Also reduced the level table size.)
Lunar Magic 3.04
SA-1 Pack v1.32
Added an UberASM code which allows you to start as Yoshi. Otherwise I saw no issues. Well, except for a weird glitched cape tile on SA-1 but I couldn't reproduce it.
Okay, but which ASM code is it a part of? Gamemode? Level? Misc?