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.
- Read the second Orbis Arcesso and then go fight Amdusias.