Your Undertale server, with the useful bits included.
Host your Undertale server
Undertale is available for Minecraft server hosting with CreeperHost.
This is a WIP map with all the mods used included for 1.17.1, to have the full experience, download optifine 1.17.1 and install it into .minecraft (you need java 8 or more installed, there are many tutorials), than it will automatically run in the modpack (even though optifine is not working with forge 1.17 currently). the only part of the map that is finished is the intro, but the pacifist run should work in less than a month
sorry, but since my exams are getting harder and I'm spending too much time of pixel art and other stuff I'm not able to complete this currently, I may come back to this project in the future but I can't promise anything
Got questions? 
Yes. CreeperHost modpack pages link into ordering with the selected pack ready to install. You can also change versions or pick another supported pack later from CreeperPanel.
CreeperPanel is built around real modded servers, including update paths that aim to preserve user configuration changes where supported instead of treating every update like a fresh install.
Eco can work for lighter packs, but Premium is the recommended CreeperHost range for modded Minecraft. Premium gives stronger hardware, Turbo Start, Bonus Memory, and Ask Theo where enabled.