In Part Six of Ian Jennings's series on creating a multiplayer game with JavaScript, the focus is on developing a matchmaking algorithm that allows users to challenge each other directly, enhancing interactivity beyond random or skill-based matchmaking. The blog post details the process of making users clickable for selection, establishing communication via a handshake, and differentiating message types to handle various interactions like chat messages and challenge requests. The algorithm involves using PubNub's publish feature to send challenge requests, which are filtered by type and target, allowing users to accept or deny challenges. This pattern of user synchronization is applicable in various contexts, such as video calls or ride-sharing apps. The article also suggests the potential for private channels to maintain challenge privacy, with further details to be explored in subsequent parts of the series.