HKMP addons are Hollow Knight mods specific to the HKMP multiplayer mod, to add multiplayer-specific minigames or other features. Most are made using the HKMP API.
Before using addons, keep in mind there are two different types of addons:
A list is in the HKMP website’s addons page. New addons can be made at any time, so the list may not have all the addons that exist.
You can install addons with the Lumafly or Scarab mod installer. The mod installer is also used to install HKMP itself, and guidance for using a mod installer is in the main page of this guide.
Insert the dll file of the addon into the same folder as your standalone server exe. You can get the dll file from your own mods folder (click ‘Open Mods’ in a mod installer).