Remember the quarter Parzival won for a perfect game of Pac-Man back in Chapter 22? Turns out it was an extra life. Instead of his avatar, and everything with it, being deleted at death, Parzival lives on.
The Sixers had detonated the Cataclyst, an artifact that pretty much nukes everything nearby, like half the population of OASIS that was watching this incredible battle. That explains the noise.
It's good that Parzival lived. It's bad that the Castle was also destroyed. Now the Third Gate is just kind of dangling from space.
Parzival needs an artifact to help him fly up to the gate. Luckily, artifacts are indestructible, and Art3mis's magic flying sneakers (no joke) are nearby.
He pretty much has one shot to ace the Third Gate, or the Sixers will win the game, and control of the OASIS. With the tension at its highest, Parzival flies into the air, and through the Third Gate.