On the everpresent question: I think we should go with change shape if we follow the example of the only genie with those abilities (efreet).
DR 5/magic? Replace polymorph self with change shape, I guess. So invisibility and shocking grasp as at will SLAs?They can only be struck by magical weapons. Great ghuls can use each of the following spell-like abilities at will: bestow invisibility, polymorph self, and shocking grasp.
Create spawn limited to jann?Only jann slain by great ghuls become ghuls themselves; all other races are simply slain and devoured.
Climb speed or just Climb skill bonus (maybe a variant with lower bonus or no climb speed?) Something like the monk's Slow Fall?Great ghuls live in seclusion in ruins or caves found in the emptiest deserts or on the highest mountains. Because of their sharp claws and incredible strength, great ghuls from the mountains are able to climb sheer rock walls that would daunt most mountaineers. Desert ghuls are not as adept at this, but can dig through sand or soft stones. All ghuls take only half damage from falls.
DR 5/magic? Replace polymorph self with change shape, I guess. So invisibility and shocking grasp as at will SLAs?
Create spawn limited to jann?
Climb speed or just Climb skill bonus (maybe a variant with lower bonus or no climb speed?) Something like the monk's Slow Fall?
Since it's only a throw-away reference, let's not do variants except perhaps in flavor text. Climb speed is good.
No matter what form they take, however, their feet always remain those of a donkey, though they often wear special boots or long robes to conceal this aberration.