As the name might suggest, Hollow Knight Multiplayer (HKMP) is a multiplayer mod for the popular 2D action-adventure game Hollow Knight. The main purpose of this mod is to allow people to host games and let others join them in their adventures. There is a dedicated Discord server for the mod where you can ask questions or generally talk about the mod. Moreover, you can leave suggestions or bug reports. The latest announcements will be posted there.

A community-made guide exists to get started easily with the mod. If you are not experienced with Github and/or Hollow Knight modding, this is the recommended way to start using the mod. Alternatively, the sections below illustrate how to get the mod from the installer or install it manually.

The latest version of the mod can be found on Lumafly, a modding installer for Hollow Knight 1.5. Using this link will automatically download the correct version of the Lumafly installer for your OS. This installer will then automatically download the modding API and you can install the mod via an easy-to-use interface.

The mod works through the Hollow Knight Modding API. After installing the API, this mod can be installed by dropping the compiled DLL into your mods folder, which can be found in your Steam installation: (Beware that these are the default locations. Your install may be on a different drive, in that case change your path accordingly.)

• Windows: C:\Program Files (x86)\Steam\steamapps\common\Hollow Knight\hollow_knight_Data\Managed\Mods\
• Mac: ~/Library/Application Support/Steam/steamapps/common/Hollow Knight/hollow_knight.app/, then click "open package contents" and content -> resources -> data -> managed -> mods
• Linux: ~/.local/share/Steam/steamapps/common/Hollow Knight/hollow_knight_Data/Managed/Mods/

The latest version of the compiled DLL can be found on the releases page.

The main interface of the mod can be found in the pause menu in-game. There is an option to host a game on the entered port and an option to join a game at the entered address and entered port. Playing multiplayer with people on your LAN is straightforward, but playing over the internet requires some extra work. Namely, the port of the hosted game should be forwarded in your router to point to the device you are hosting on. Alternatively, you could use software to facilitate extending your LAN, such as Hamachi.

The interface can also be hidden by pressing a key-bind (right ALT by default). This key-bind can be changed in the config for the mod, which can be found at the following locations depending on OS:

• Windows: %appdata%\..\LocalLow\Team Cherry\Hollow Knight\HKMP.GlobalSettings.json
• Mac: ~/Library/Application Support/unity.Team Cherry.Hollow Knight/HKMP.GlobalSettings.json
• Linux: ~/.config/unity3d/Team Cherry/Hollow Knight/HKMP.GlobalSettings.json

The key-binds are stored in keycode form, please consult this list for all possible keycode options.

In addition to the pause menu UI, there is a chat window that allows users to enter commands. The chat input can be opened with a key-bind (T by default), which feature the following commands:

• connect <address> <port> <username>: Connect to a server at the given address and port with the given username.
• host <start|stop> [port]: Start a server on the given port or stop an existing server.
• list: List the names of the currently connected players.
• set <setting name> [value]: Read or write a setting with the given name and given value. For a list of possible settings, see the section below.
• announce <message>: Broadcast a chat message to all connected players.
• kick <auth key|username|ip address>: Kick the player with the given authentication key, username or IP address.
• ban <auth key|username>: Ban the player with the given authentication key or username. If given a username, will only issue the ban if a user with the given username is currently connected to the server.
• unban <auth key>: Unban the player with the given authentication key.
• banip <auth key|username|ip address>: Ban the IP of the player with the given authentication key, username or IP address. If given an auth key or a username, will only issue the ban if a user with the given auth key or username is currently connected to the server.
• unbanip <ip address>: Unban the IP of the player with the given IP address.

Each user will locally generate an auth key for authentication and authorization. This key can be used to whitelist and authorize specific users to allow them to join the server or execute commands that require higher permission.

• whitelist [args]: Manage the whitelist with following options:
  • whitelist <on|off>: Enable/disable the whitelist.
  • whitelist <add|remove> [name|auth key]: Add/remove the given username or auth key to/from the whitelist. If given a username that does not correspond with an online player, the username will be added to the 'pre-list'. Then if a new player with a username on this list will login, they are automatically whitelisted.
  • whitelist <clear> [prelist]: Clear the whitelist (or the pre-list if prelist was given as argument).
• auth [name|auth key]: Authorize the online player with the given username or auth key.
• deauth [name|auth key]: De-authorize the online player with the given username or auth key.

It is possible to run a standalone server on Windows, Linux and Mac. The latest executable of the server can be found on the releases page. For Linux and Mac, the server can be run with Mono installed. After installing Mono, the same executable can be run using mono HKMPServer.exe <port>. Currently, the only command-line argument is the port that the server should be hosted on.

Alternatively, a Docker image is available on DockerHub (courtesy of maximalmax90).

The server will read/create a settings file called serversettings.json, which can be changed to alter the default startup settings of the server. Alternatively, settings can be changed by running the settings command on the command line. In addition to the commands described above, the standalone server also has the following commands:

• exit: Will gracefully exit the server and disconnect its users.

There are a lot of configurable settings that can change how the mod functions. The client settings are available in the pause menu UI of the mod, while the sever settings can be changed with the settings command.

The client settings contain the following entries:

• Team Selection: Allows the player to change their current team. This setting can only be changed when it is enabled server-side.
• Player skin ID: Allows the player to input the ID of the skin they would like to change into. After pressing the "Apply skin" button, this will locally change the skin and transmit it to the server. This only has effect if skins are enabled on the server.
• Display ping: Whether a ping display is enabled in the top-left side of the in-game screen. This will display the current RTT (round trip time) of the client-server connection.

This section contains the settings for the server. These values can be read and modified by the set command described above. All names for the settings are case insensitive, but are written in case for clarity.

• IsPvpEnabled: whether player vs. player damage is enabled.
  • Aliases: pvp
• IsBodyDamageEnabled: whether contact damage is enabled, namely when player models touch, both of them will be damaged. This only has effect if PvP is also enabled.
  • Aliases: bodydamage
• AlwaysShowMapIcons: whether player's map locations are always shared on the in-game map.
  • Aliases: globalmapicons
• OnlyBroadcastMapIconWithWaywardCompass: whether a player's map location is only shared when they have the Wayward Compass charm equipped. Note that if map locations are always shared, this setting has no effect.
  • Aliases: compassicon, compassicons, waywardicon, waywardicons
• DisplayNames: Whether overhead names should be displayed.
  • Aliases: names
• TeamsEnabled: Whether player teams are enabled. Players on the same team cannot damage each other. Teams can be selected from the client settings menu.
  • Aliases: teams
• AllowSkins: Whether player skins are allowed. If disabled, players will not be able to use a skin locally, nor will it be transmitted to other players.
  • Aliases: skins
• AllowParries: Whether Nail slashes and Nail Arts can be parried. Only applicable when IsPvpEnabled is true.
  • Aliases: parries

The rest of the settings contain entries for damage values of most PvP enabled spells and abilities. Setting them to a value of 0 will completely disable the damage. Following is a list of the setting names for these along with their aliases in the parentheses:

• NailDamage (naildmg)
• GrubberflyElegyDamage (elegydmg)
• VengefulSpiritDamage (vsdmg, fireballdamage, fireballdmg)
• ShadeSoulDamage (shadesouldmg)
• DesolateDiveDamage (desolatedivedmg, ddivedmg)
• DescendingDarkDamage (descendingdarkdmg, ddarkdmg)
• HowlingWraithDamage (howlingwraithsdamage, howlingwraithsdmg, wraithsdmg)
• AbyssShriekDamage (abyssshriekdmg, shriekdmg)
• GreatSlashDamage (greatslashdmg)
• DashSlashDamage (dashslashdmg)
• CycloneSlashDamage (cycloneslashdmg, cyclonedmg)
• SporeShroomDamage (sporeshroomdmg)
• SporeDungShroomDamage (sporedungshroomdmg, dungshroomdmg)
• ThornOfAgonyDamage (thornsofagonydamage, thornsofagonydmg, thornsdamage, thornsdmg)
• SharpShadowDamage (sharpshadowdmg)

Skins can be installed by dropping a folder into the skins directory (<steam>/Hollow Knight/hollow_knight_Data/Managed/Mods/HKMP/Skins). If this directory structure is not present yet, it should be generated once you have launched the game at least once with HKMP installed. This folder can be named anything, but the files should be texture sheets that Hollow Knight also normally uses. After running the game with skins installed, each of these skin directories should have a corresponding id.txt file generated. This ID file contains a single integer representing the ID of that skin. This ID can then be used in-game to select the skin from the client settings menu. Normally, these IDs start at 1 and incrementally increase the more skins you use, but it is possible to manually edit the ID files to use other IDs.

There are a few ways you can contribute to this project, which are all outlined below. Please also read and adhere to the contributing guide.

If you have any suggestions or bug reports, please leave them at the issues page. Make sure to label the issues correctly and provide a proper explanation. Suggestions or feature requests can be labeled with "Enhancement", bug reports with "Bug", etc.

The HKMP mod can also be built from scratch. This requires a few dependencies from the Hollow Knight game and the modding API. Namely, the following assemblies are needed from the modding API:

• Assembly-CSharp.dll (modified by the modding API)
• MMHOOK_Assembly-CSharp.dll
• MMHOOK_PlayMaker.dll
• MonoMod.Utils.dll

And the following assemblies are needed from the Hollow Knight game/Unity:

• PlayMaker.dll
• UnityEngine.AudioModule.dll
• UnityEngine.CoreModule.dll
• UnityEngine.dll
• UnityEngine.ImageConversionModule.dll
• UnityEngine.InputLegacyModule
• UnityEngine.ParticleSystemModule.dll
• UnityEngine.Physics2DModule.dll
• UnityEngine.TextRenderingModule.dll
• UnityEngine.UI.dll
• UnityEngine.UIModule.dll

All the files above can be found in the following directory based on your operating system (and might vary depending on installation):

• Windows: C:\Program Files (x86)\Steam\steamapps\common\Hollow Knight\hollow_knight_Data\Managed.
• Mac: ~/Library/Application Support/Steam/steamapps/common/Hollow Knight/hollow_knight.app/, then click "open package contents" and content -> resources -> data -> managed
• Linux: ~/.local/share/Steam/steamapps/common/Hollow Knight/hollow_knight_Data/Managed

With these assemblies handy (either in their original Hollow Knight directory or moved somewhere else) you should copy and rename the HKMP/LocalBuildProperties_example.props file to HKMP/LocalBuildProperties.props and fill the paths in it to your locally used paths. After this the source code can be compiled into a DLL, and you should be good to go!

The standalone server can also be built from scratch. There are technically two dependencies for the server:

• The built HKMP mod DLL (HKMP.dll)
• The Newtonsoft JSON library DLL (Newtonsoft.Json.dll)

The HKMP mod DLL is linked from the Release directory of the mod project and does not have to be manually copied. The Newtonsoft JSON library, however, can be found in your modded Hollow Knight installation as denoted above. This DLL should be placed in the HKMPServer/Lib/ directory and will be embedded together with the HKMP DLL during the build process.

Make sure to first build the HKMP mod before building the server to ensure the latest version is embedded.

If you like this project and are interested in its development, consider becoming a supporter on Patreon. You will get access to development posts, sneak peeks and early access to new features. Additionally, you'll receive a role in the Discord server with access to exclusive channels.

HKMP is a game modification for Hollow Knight that adds multiplayer.
Copyright (C) 2023 Extremelyd1

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