I just noticed it when I was about to place my Dark Rift in my vault.

It's a minion battling system. I haven't been following the thread, so that's about all I know. Not all minions have stats yet as it's still in testing (or, at least they didn't originally). I think they might use it as a way to get older retired minions into the economy in the future, but I don't think that was certain yet? You're able to take minions back out whenever you like though, and I think you can add doubles so it's a little like a minion collection but not as permanent.

That sounds like fun. Thank you very much for the information.