Successfully complete the game and save the game. Instead of starting a new game, load your completed game file. Proceed to the location where you had to open two locks to open a gate. When you get the choice, move towards the left path. Locate the Metatron on the far west side of the left path on your map. Go to the Metatron. There is a dead end behind it. Fly close to it and look for cracks on that wall. Shoot this part of the wall, then enter the tunnel that is revealed. Defeat Anubis and collect his icon to unlock Auman Anubis. Note: You will have to fight Nepthtis immediately after this battle.