Begin by entering the following code: ?QDM 7HYC BB4X FJVB, once you are loaded into the level hit start and choose the Features option and warp to the Final Judgement level. The level itself is pretty straight forward, pick up the supplies in the first room and then head out into the court area. I highly recommend killing most of the enemies here as they can become a problem if left alone. You need to collect the 3 demon artifacts to open the gate in order to fight the boss. The keys are scattered in rooms on the outer rim of the level and are easy enough to find. Save your energy ammo for the final boss fight and use the Unmaker when fighting her.
Here is a video or those needing hep with the locations of the keys: