...that I haven't seen before, and it's not the swimming in the air glitch either.
Watch it, and you'll see, I don't even know how he activated it, I think it was because he died in an unexpected spot?
I think it's around 5:47... He died trying to perform swim in air, then he was returned to the checkpoint(before the drawbridge), but even though all the enemies were dead the drawbridge wasn't open.