I'm guessing he might get wings, and this might bring him into conflict with whatshername the winged goblin saviour lady and it turns out that just as THAC0 was meant to be chief his son was meant to be uberchief.
Plus we'll probably find out that this means Complains is rocking PC stats plus the bonus for being chief plus whatever the Fiendish template gives you, and he'll think he's lost his soul but hasn't got some reason. Goblins trends towards ridiculous power boosts almost as much as appearance changes.