Villainous Competition XX​III: Two Heads Are Better Than One

[Thurbane]

Maybe this is another tangent, but are you sure the Half-Fiend template works this way? Usually, template abilities don't scale with class levels. For example, the Book of Exalted Deeds discusses on p. 27 how to modify the LA of the Half-Celestial template based on the creature's racial HD, and it seems to assume that there is no scaling of the template's abilities beyond what you start with: so a base-race creature gets a static LA +2 for Half-Celestial.

Not sure what BoED has to say, just going by my reading of the SRD:

Challenge Rating
HD 4 or less, as base creature +1; HD 5 to 10, as base creature +2; HD 11 or more, as base creature +3.

AFAIK, the template checks total HD, not purely racial. If there's a specific rule about this somewhere, it would change my understanding of how it all works...