I was working on something that was (at first) just a little WAD that I was gonna use without sharing because It's my first WAD file in progress, but screw that, I'm sharing it.
It just changes SRB2 music to Undertale music. Some examples include:
Green Flower Zone - Ruins
Techno Hill Zone - Core
Deep Sea Zone - Waterfall
Red Volcano Zone - Hotland
Super Sonic - Megalovania
Invincibility - Song That Might Play When You Fight Sans

It's a basic WAD. Nothing special. It's basically a test. I'm testing to see if I'm capable of finishing a WAD for SRB2. If this ends up being successful, I'll move on to making a character, if that's a success, I'll move on to a level.