NidhOX

Nidhogg Open-source eXperience: a two-player fencing game played in a terminal on Cauldron, from your own copy of the game's files.

No game files are included. NidhOX reads the data file of a copy you own — data.win from the Windows build, or game.ios from inside the macOS build's Nidhogg.app — and draws its rooms from it. It also reads the game's executable installed with it (Nidhogg.exe beside data.win, or the app's MacOS/Nidhogg) for the depths the game creates its objects at and its news; a data file without it does not start. The languages come from the copy's lang folder, and the search screen's lines from its match.txt.

Each NidhOX release plays one version of the game. Use the release that matches your copy:

Steam updates your copy unless you held it back, so most copies are on the Online Update. NidhOX 0.2 was checked against that update's first build (Steam build 25889827, 13 October 2026); its patch of 16 October 2026 ("The Waiting Game", build 25998581) has not been checked yet.

mix deps.get
mix nidhox
mix nidhox --area Wilds
mix nidhox --data path/to/data.win

--data defaults to NIDHOX_DATA, then the first of the usual Steam installs under your home directory: CrossOver's, macOS's and Linux's (set in config/runtime.exs). --area is the area the level select starts on: Cemetery (the default), Castle, Mines, Sky or Wilds.

Controls

Two players share the keyboard, or play with a controller each:

In the menus, either side's keys work: up and down move, jump or start chooses, and Esc (a controller's B) goes back. The prompts in each box show the keys and buttons of the player using it. Ctrl+Q quits at once.

Controllers take the free sides in the order they connect; Options → Controls → Controllers lists the connected ones and moves each between player 1, player 2 and none, and the choice is kept for that controller.

Modes

NidhOX opens on the logos, then the main menu. Press start to open it. Left alone for twenty seconds, the computer plays a match against itself on one of the five areas; any key brings back the menu. A white dot marks what is new, and News while an article is unread.

• Multiplayer
  • Local: two players at one keyboard, or a controller each. The level select pans across the map; up and down pick the area, jump or start starts the bout, and Esc asks whether to go back to the main menu. After a bout the match statistics show; up or down switches their bottom line between going on and watch replay, which plays the bout again (Enter skips it).
  • Online: see Playing online.
  • Tournament: 3 to 8 players taking turns at the two sides, single elimination. Its window shows the bracket as it will start. Set Players and the Map with left and right, the Variants, then Start tournament. The ladder shows the bracket, the next two players flashing; a player drawn against an empty place (X) goes through. Start or jump leads to a nine-second warm-up in which the next two find their controllers and can already fence, then their match; the first of the two plays yellow. The last player left is the champion.
• Options: the language, Controls to remap each player's keys, flashing and persistent blood on or off, and music and sound effect sliders (left and right; the effects level scales the music too). They are kept in your settings, ~/.config/nidhox/<name>.settings. They are on the pause menu as well.
• Extras
  • How to play: the game's lessons, one at a time, with an orange dummy. Each instruction shows your own keys.
  • CPU battle: the computer against itself. Set Hype (how well both play), the Time limit and Sudden death only, then Begin. The level select picks an area at random and starts by itself after 45 seconds; the results go on by themselves after 15, round and round until you leave from the pause or the level select.
  • Credits: from your copy's credits.txt.
  • Challenge: you against a computer opponent that gets harder each time you kill it. Every move that lands scores its worth: lunge, snap, kick, punch, sweep, guard, parry, throw and dodge. A move's worth halves each time you use it and climbs back while you use others, so vary them. Dying ends the run; your best score is shown along the bottom.
• Quit to desktop: asks first.
• News: the game's articles. Choose one to read it; up and down scroll it. An article's video is named where the game plays it; select on its link puts the link on your clipboard.
• Single player
  • Arcade: sixteen bouts against the computer across the Mines, Sky, Wilds and Castle, each against a different opponent and harder as you go. Lose and you fight that opponent again; win the last and the game is complete, with your time.
  • Training: you against the computer on side 2. Pick its personality, then its difficulty (left and right), then the area on the level select.

Enter or Esc during a bout pauses it: unpause, change level, variants (changing the time limit or sudden death asks to restart the match), change color (each side's colour from eight), options, and exit, which asks first. After a bout come its time, the winner, and each side's kills and suicides; any press goes on to the level select. Every bout's result is kept, per player, in ~/.local/share/nidhox/ledger.dets.

Playing online

Multiplayer → Online opens the online menu. While it shows, this machine keeps a lobby open on the local network that friends can join.

• Find a match searches the local network. It joins the open lobby with the lowest ping, or opens one and waits. When two players meet, both see MATCH FOUND! with the other's name and ping: both press select within ten seconds to play. Back denies; the denier stops searching and the other goes on searching, passing over the denier for 30 seconds.
• Invite friend lists the players heard on the local network and your recent opponents. Choose one in the game to join them, or any other to invite them: they see INVITE! for 30 seconds on their menus.
• Host over SSH serves the game over ssh. It first asks for the port: leave it empty for any free one, or type one (NIDHOX_SSH_PORT or mix nidhox --ssh-port fills it in). It then shows the command to give the other player: ssh -p <port> new@<address>. They need only an ssh client, no copy of the game. The first time, any password opens a form where they pick a name and password, and they connect as that name from then on. They play orange in this machine's game, in their own terminal; sound reaches them only through an ssh -R tunnel to a player program on their machine. The game reaches them at 20 frames a second, fewer on a connection too slow for that. Going back stops serving; they are disconnected with their terminal put back as it was and a line saying the host stopped.
• Join by address types the address and port a lobby shows under the online menu, address:port, to join a machine the local network cannot hear, such as one across the internet. That machine starts with a fixed port (mix nidhox --port 9200) and opens that TCP port.

Two players who meet play in the lobby: each stands in their own half and readies up by standing on their ready zone. Once both have stood there for a second, the loser of the last match picks the area, and the match is played. Its results wait for both players, and the lobby comes back, with each player's wins tallied. In the lobby, start opens the pause: Input delay sets how many frames ahead your input is sent, green when it covers the ping. Leaving the lobby or the level select ends the session for both; in a match, the pause's Forfeit gives it to the other player.

Each machine runs and draws the game itself, playing with rollback. The two exchange only the players' joins, leaves and input over one TCP connection, and nothing the other machine sends can run code on yours.

On a terminal that keeps images, how the picture is sent can be chosen when starting the game, for every player including those over ssh, with mix nidhox --picture (or NIDHOX_PICTURE) and any of, comma separated: native draws the room at its own size times the largest whole number that fits the window, or native:2, native:3, … at that many times; size:WxH sets the size itself; png sends each frame as a PNG, smaller; swap replaces each frame without the picture going blank in between. The default is native:2,png,swap; --picture none sends the picture at the window's cells as raw pixels instead.

Where the machine has a graphics card, it draws the picture: the same picture, pixel for pixel at the whole-number sizes native picks, in about a sixth of the time at large sizes. Without one the game draws it in software. The picture options choose otherwise: software draws in software, gpu asks for the card in the terminal, and window opens a window of its own whose keys play the game, as in --picture native:2,png,window.

How it plays

Two fencers start in the middle of an area. Yellow wants to reach the far right end, orange the far left.

• Stance. Up and down move your sword between high, middle and low. A thrust is parried by an opponent who faces you with the sword at the same height; it kills one holding it anywhere else.
• Disarm. Moving your sword into the height of a thrust just before it lands knocks the attacker's sword away.
• Throw. Hold up in high stance and attack to throw your sword. It kills whoever it reaches, unless they face it with their sword held high.
• Unarmed. Without a sword, attack is a punch that knocks the opponent's sword away. Duck over a sword on the ground to pick it up.
• Right of way. Killing your opponent lets you run on towards your goal; the camera follows you, and your opponent comes back ahead of you. Only you can leave the screen, into the next room. Falling into a pit hands the right of way to your opponent.
• Winning. Reach the goal at your end of the area. The next bout starts in the middle.

The rooms, their scenery and ground, the fencers, the menus and their lettering, the sounds and the music all come from your copy of the game.