You need to strip Amdusias of his dragon form in order to kill him, loot him, jump on his dead body a few times, and then continue.
- You must enter the Bedroom Quarters and collect all of the keys from the rooms upstairs. Then go to the lower level of the Bedroom Quarters and find a Chest that is beside a lit candle. Inside, it will contain the Orbis Arcesso that is needed to continue.
- Read the Orbis Arcesso, then return to the Librarian and ask to read the second book to learn you need a phial of Amdusias' blood and Dragon Scales to strip him of his dragon flying ways.
- You need to return to the Bedroom Quarters, enter Amdusias' Room, and 'use' the book located on his bookshelf to unlock his hidden room which contains a Phial with blood (that is needed for the quest) as well as a chest that can be unlocked by mind reading Amdusias.
- After obtaining the Phial, you need the Dragon Scales. I recommend saving next, because you'll probably die a few times.. The Dragon Scales are located in the Blood Altar room which is guarded by Amdusias and his dragon fireball shooting self. Prepare a potion or two and sprint towards the green glowing scales on the ground at the end of the skeleton path, steal it, and then run back. (you can cheat by closing the door on the left and stepping back a bit before re-entering. Amdusias then gets stuck in an animation loop and won't fire at you)
- Read the second Orbis Arcesso and then go fight Amdusias.
After killing him and jumping up and down on his.. well, what was once his body.. you will finish the quest and receive a default reward of 1100 exp, 180 gold and one choice from another 1100 exp or 180 gold.