He gets 3 new lvl 9 spells, two of which are fuelled by nostalgia for his mortal life, an aura that grants his allies +10 to ability checks and some boosts to his stats that I don't recall the details of. You also get several dialogue variations when chatting with your former companions.
Edit: I had a peak, he gets +7 to Int and +4 to all remaining stats.
Can you make screenshots please? Stats and spells & effects description
Does his HP also increase?
