As far as I know, this doesn't work the same on North American version. The idea is to get to the boss with any amount of gold, which baits the Goblin King at the point where he should despawn due to the boss trigger. I've gotten a variety of glitches from pulling this off, but never to the results I've seen on JP or EU versions. Either way, this trick is not easy and it was fun to watch on this vid :)