Ah, the tyranny-based effects for the Battlefiend would work well. I was kind of scratching my head on what to add. I think I'll replace Sneak Attack with some more dominating effects. He's supposed to be the mostly-honorable bad guy who's looking for a worthy opponent that can weather his mastery of techniques and sheer presence.
The Warstomper did lack a bit of divine intervention for the most part. I'll tweak that as that was one facet of this project.
Hound of Orcus this was a necromantic prestige class I had created earlier and decided to include here. I was looking to make undead army building more than just Destructive Retribution. I'm also a bit of a fan of transformational sorts of PrCs.
I like your idea for the Sentinel. As is, it's mostly a knowledge gatherer but doesn't do much to put that to use. Driving the enemy mad with stolen secrets from the forgotten halls of fallen demon lords would be a blast. Maybe I could somehow combine the Absorption ability with that: more powerful information leads to a greater effect based on the DC to Decipher it or find out about it through Lore. All in all, it didn't quite reach what I had wanted it to be so far (the ideal I was reaching for here was my favorite out of this group).
And the Slaughterguard was made to be the guy you see coming at you from the opposite end of a skirmish and make you want to run away. That set-up in designing the class, getting to choose abilities from a list like that as you wish to choose them, has also been one of my favorite ways of distributing class abilities in prestige classes.
I'm also still trying to work on a prestige class for Nerull. The Reaper niche has been done time and time again for his associated classes. So, I was thinking something else. Or maybe just try my darndest to set the bar above what's been done before. For me, at th end of the day all PrCs should give out equal utility over a number of situations; the intrigue comes from the unique abilities that change your focus beyond the normal archetypes of RPGs that can be done to lesser extents with alternate builds.
As always, anyone can use these classes for their own devious means. I only wish to hear about how it went. They're intended for NPC use, but some less so than others.