I see many good suggestions, though I think it could be a otyugh/glabrezu combo.Do you have the Advanced Bestiary? I'd love to have a look at the amalgam template, and that is one book that I never see used.
No, I have yet to get either Advanced Bestiary or Tome of Horrors though from what I see of the recomendations folks are making, I will make a point of getting them.