I wonder if there's a (preferably legal) way to get my hands on the tileset and music files (for Rivals of Aether custom stage purposes).
Viewing post in Devlog 1/16/23: Progress?!?! comments
The tilesets and 90% of visuals (not including KeyPick assets) were made by me, and you can feel free to use them. I think the quickest way to nab them would be to get a GMS decompiler such as UndertaleModTool, unzip the game exe (it's a self-extracting exe so you can do that), and then open the data.win file with UndertaleModTool to look at all the assets. As for the songs, those are credited in a readme file, and you can probably find them through more conventional means.
Update: Stage is finished! No scripting, sadly (or, at least, not yet).
https://steamcommunity.com/sharedfiles/filedetails/?id=2920964094