Discord-Tampermonkey
I DO NOT OWN ANY OF THIS! ALL CREDIT GOES TO THE DISCORD.JS DEVS, BROWSERIFY DEVS, AND UGLIFY DEVS.
This is a version of Discord.js, linked here: https://github.com/hydrabolt/discord.js that I converted with Browserify to work in the browser, and Uglified to minimize file size.
Include this in your Tampermonkey scripts with // @require https://cdn.rawgit.com/Mega-Mewthree/Discord-Tampermonkey/25c3c745/browser.js.
For reference, go to https://discord.js.org.