Creating a fast and scalable online multiplayer game for web browsers involves numerous challenges, such as ensuring cross-browser compatibility and maintaining fluid real-time gameplay across various devices. This tutorial walks through the process of building "Ninja Platformer," a browser-based collaborative puzzle game using less than 1000 lines of code, employing Phaser, an HTML5 game development framework, along with JavaScript, HTML, and CSS. The guide details setting up a development environment with tools like Visual Studio Code, Node.js, and a local web server, as well as integrating PubNub's API for real-time data synchronization, enabling multiplayer functionality. By following the step-by-step instructions, users learn to manage game states, handle player input and object collisions, and implement multiplayer features using PubNub’s Functions feature, which captures events on the PubNub Platform and ensures consistent gameplay across different client sessions. In the end, developers gain insights into creating engaging multiplayer experiences, with opportunities to explore further enhancements such as in-app chat and real-time leaderboard updates.