Both mods worked fine on my client test world and fixed the issue I was having with the ender tether, but once I tried to load it up on my server I started getting this crash on startup: https://pastebin.com/aYc6zABs

• DarkUtils-1.12-1.6.160
• Bookshelf-1.12-2.0.0.412

Thanks for the report, a new build will be automatically uploaded to Curse soon. Mojang keeps doing really weird things with their color code formatting. It will be live here