This tutorial will teach you how to use Multiplayer Instances with shared variables in your game.
Use the Keeping Score Blocks from Getting Started. Here are the starting Blocks:
Change the instance variable from GLOBAL to SHARED.
Get the When Variable is Changed or Initialized Block from the Events Drawer.
Move the Set Text Block to the When Score is Changed or Initialized Block.
Now the text of the scores on game instance 1 and game instance 2 should change simultaneously and show the same score.
On the Design Screen, go to Game Properties.
Check "has multiplayer instances".
In the next page, we will play the game using two tabs in the browser.