Fiendish Aspects, Part 1

From Introduction:

So, you've seen the half-fiend template in the Monster Manual (D&D 3.5e), but you want to add a bit more variety to your half-fiends. Take a look at this series of web enhancements that suggest how you can do that. You'll find basic rules for making your half-fiend more like the base fiend that you choose to use, plus you can start implementing these rules right away by using the statistics for several half-fiends that are within these PDFs.