Thutmose

Once you enter Thutmose's lair you will be greated with the Projection of Thutmose. Once the projection has been slain. You will be blinded (regardless of blind protection) and teleported. Once you can see again, you will see that the back wall of the room containing the Projection is now open and you are just behind where this wall would have opened. In addition to Thutmose himself, he will be accompanied by two companions. One ranged, one melee. The two companions hit more consistently and harder than Thutmose and should be focused if possible. Alternatively, you can potentially drag Thutmose to the bottom of his lair if you have not yet been seen by the adds after becoming unblinded to simply avoid them.