To use this, open the developer console, enable pasting, and copy+paste the script. Open the emoji picker (make sure all the servers you want included are un-collapsed) and scroll to the top. Leave it open and run getEmojis(); in the console. It will scroll through the list, moving down every 750ms. Once it either reaches the bottom, or you're satisfied with the number collected, run finished(); and copy the output. Paste it into a file in an empty folder and execute it as a Linux shell script (/bin/bash or similar). It will create a folder for each server, then download all of their emojis.
Based on https://gist.github.com/junebug12851/8c5c42587a824c22a79359fb56b4023d