Story related and cannot be missed.
This unlocks after defeating the Grandmaster’s final game at the end of the fifth episode, “Soul of a Maze”. To do this and win the stone, you need to open the center glass console by hacking the 3 terminals. Sounds simply enough but it gets frustrating due to the constant attack of enemies and the cloning of enemy versions of yourself.
This is what I did that finally worked but it is still annoying on Hard. First, clear out the enemies and use Iron Man to hack the first terminal. You can do them in any order but I started with the middle. Then use Wolverine and slash the 3 posters in the back when they are green to prevent some of the minions from materializing. Switch back to Iron Man and quickly hack another terminal. Fight more clones and minions and then quickly hack the final terminal. Now watch out for all the vortexes that spring up and as soon as the glass console is open, jump in and claim your prize. If you do get knocked out, just run over and revive the fallen character with .