You will see darkness once you enter the battle, but get behind pillars as fast as you can. You will be given a gun, and you must shoot The Last Hurdle Monster. If you die do not panic, as you spawn right outside. Do not try to open the doors, as it won't work when there is a battle inside.

Once the monsters health goes down half way, stones will appear, and lava will flow on the floor. So you must jump onto the stones, then shoot the monster, and avoid the bombs he throws at you.

Once you kill him, you get the badge and another surprise, you get kicked, hooray! So I suggest you reset after you get the badge, if you want to stay in game.