I've had this one cooked up for awhile but it used the lich template instead of true ghoul.
Take yourself a typical Androsphinx. Good magical beasts that cast cleric spells and can do roars that are normally only effective if they don't happen to have any allies around.
Now, add your true ghoul template to it and surround him with some undead associates. Voila: His associats are immune to his fear roar, his paralyzation roar, and his ability damage roar.
But for true rat bastardness, advance your evil ghoul androsphinx to 22 HD. He now casts as an 11th level cleric (normal andros are 12 HD and cast as 6th level clerics. 12/2 = 6. 22/2 = 11. just explaining my logic although I don't know if it actually works that way. Besides, you're the DM it can work any way you damn well want it to!)
The point is, since he has access to the Protection domain, he can now cast Antimagic Field on himself after he's done roaring, bolstering his undead buddies and other nastiness, then walk into melee. Since he's 22 HD, he's got a lot going for him.
1.) Advanced a size category, lots of bonuses there (namely his str is now base 33)
2.)Magical beasts have Fighter BAB, so he starts at +22 to hit.
3.)A huge true ghoul (using
this link you provided earlier ) does 2d6 base damage with his claws, +11 from his strength.
4.) 22d12 + 132 Hit points
5.) 10' reach
6.) Lots more feats to do nasty things with when he goes melee (improved disarm anyone? improved grab?)
7.) IMC, I would increase the DC of his roars because of his advancement. I was never able to decide what that should be, but enough to be at least some worry to characters worthy of facing him.
This also exploits the fact that the Defenders don't have any monks (that I'm aware of) and seem to pretty dependant on their spells and magic items. Tomtom might be a problem if you play with the "Psionics are different" house rule, because magical beast don't get better Will saves.
I would put his CR around 17 or so.
There are many other advantages which I can get into if you like the idea. I've got his full info (with some differences because, like I said, he's a lich in my version)