When you run Mirror and Socket.IO in the same Unity project, you immediately hit a translation problem. Mirror identifies players by netId — a uint assigned at spawn time by the Mirror host. Socket.IO identifies players by playerId — a string assigned by your Node.js backend when they connect. These two IDs have nothing to do with each other. They're generated by different systems at different times. But when a score_update arrives from your Socket.IO backend with a playerId , you need to find the corresponding Mirror NetworkIdentity to apply the effect. And when a Mirror player spawns, you need to register which playerId they belong to so future backend events can reach them. GameIdentityRegistry is the pattern that solves this. The Pattern A static lookup table. Two dictionaries. One clear API.…