The white house juju that claiborn found and then used it to trap(?) The beta kids in it. Then, dead vriska finds it. Live vriska uses it. But what is supposed to come out of the house? (it had a door that was about to be opened, both on the winner platform and in the dreaam bubble)

It’s hard to say what its actual function is/was, there’s a LOT of symbolism in Act 7 that can be taken in multiple ways. Many people think the trapped Kids come out of the House to beat LE up but I personally think it’s something else entirely. Maybe the Epilogue will give us some canon look at the events post Act-7.