How to make an online monster collector with turn-based battles

Net Forge, the open-source multiplayer browser game engine built for AI coding agents, is published on npm under @netforge with source at github.com/netnetdev/net-forge.

Run npm create netforge@latest my-collector -- --template collector --yes and you have an online monster collector: pick a starter at camp, walk the grass, battle wild creatures turn by turn with a team of three, catch them, and join everyone in the marsh to bring down the warden before dusk. Creatures, moves, elements and the map are declarations in src/game.ts.

npm create netforge@latest my-collector -- --template collector --yes
cd my-collector
npm run play

--template monsters is accepted as the same template.

#What you get

#1. Start it

npm create netforge@latest my-collector -- --template collector --yes
cd my-collector
npm run play -- --players 2

Walk with WASD, the arrows or the left thumb on touch.

#2. Add a creature and its moves

import { creature, move } from "@netforge/engine";

move("leaf_lash", { element: "root", power: 40 });
move("thorn_curl", { element: "root", power: 0, effect: "guard" });
move("tide_crash", { element: "tide", power: 70, accuracy: 0.8 });
creature("thistlehog", {
  model: "style.lowpoly.fox",
  element: "root",
  hp: 50,
  atk: 52,
  def: 48,
  spd: 46,
  moves: ["leaf_lash", "thorn_curl"],
  catchRate: 0.7,
});

Then put it in a grass zone's pool in marsh({...}) and add its label to src/names.json under weapons. A power of 40 is a plain hit.

#3. Shape the marsh

Grass zones decide what you meet and how often. Put weak creatures near camp and stronger ones toward the warden:

marsh({
  size: [30, 20],
  camp: [2, 10],
  grass: [{ at: [4, 2, 6, 5], rate: 0.22, pool: [{ creature: "thistlehog", weight: 3, level: [2, 3] }] }],
  // ...the template's water, blocked tiles, warden and dusk stay as they are
});

Rects are [x, y, width, height] in tiles of 2 m. Leave a walkable way from camp to every grass zone and to the warden; the build checks it.

#4. Test it

npm test

Four playtest keepers must win battles, catch creatures and fire an earn rule within four minutes, without losing their whole team more than twice each.

#How it works

The collector is a rules genre: the room runs it at 30 Hz with integer state and a seeded generator. Every roll (encounters, accuracy, damage spread, snares and the foe's move) is the room's, so a run replays exactly from its inputs. Your keeper is predicted with the same tile collision the room runs, so walking never waits. A battle is private: the room sends your team, your foe and the log only to you, and others see the creature beside you. See Make a turn-based multiplayer game and the monster collector template page.

#Alternatives

• Godot has a scene editor and tile tools suited to hand-built RPG maps, and exports to the web as WebAssembly with WebGL 2. Pick it for a single-player creature RPG with a long story.
• Phaser is a free, open-source 2D framework with WebGL and Canvas rendering. Pick it for a 2D top-down collector in sprite art.
• Colyseus is an authoritative room server with state sync, for writing the battle rules as server code against your own client.

Pick Net Forge when you want the shared-world, turn-based collector already online, with private battles and a playtest.

#FAQ

#Are battles turn-based or real-time?

Turn-based. Each turn you pick a move, a swap, a snare or flee; the faster creature acts first and the foe answers with its best move.

#Can players see each other's battles?

They see the creature beside you, not the battle. Your team, your foe and the log are sent only to you.

#How does catching work?

A snare's chance is the creature's catch rate times (0.25 plus 0.75 times the foe's missing health), so weakened creatures are easier to catch. A team holds three; more go into the lantern.

#How many players share the world?

Up to eight per marsh, all wearing down the same warden.

#Can I add more element types?

The four elements and their cycle are fixed by the genre. Variety comes from creatures, moves and effects.