Guys... why is sans undertale in my New Super Mario Bros?

Arrangement uses the instruments from sans, it's raining somewhere else, and song that might play when you fight sans.

Credits: 

Undertale Lost Archived:
For making the video that gave me the idea to do this
https://youtu.be/vGeypRZeHic

TEP: 
The guy who showed me the video (He's also a really cool composer)
https://soundcloud.com/burger-128189535

Storm:
Made the spreadsheet I used to find the instruments from the songs I listed above.
https://docs.google.com/spreadsheets/d/1eOyF0lWWKb_2q4eX7Hs80JIv6o9ZE9yWCksxCbmPTZs/edit?gid=767604283#gid=767604283

New Sans Bros. Wii OST - Overworld

monochrome