A minor one considering how few there are, but I remembered this from a bit ago, so:
Trillocks seem to give the same XP as Skeleton Knights, but I think are clearly a more dangerous foe.
In addition to their death effect and other abilities, they have a confusion bolt that is rather difficult to deal with.
Note that the confusion bolt has no save: it's just a touch attack that is pretty easy for the creature to make. (and this is using Lillia as a reference point, despite her getting a good amount of her AC as dodge via divine shield)
The only real defense is to use clarity, which with it's short duration, value of the consumable items, and spell level, makes it something that's impracticable to protect a whole party against at the levels where they still give XP (keeping in mind that the party also has to worry about death effects only makes this worse).
Keep in mind, also, that in the 3.5 monster manual, they're CR8 (& level 8 I think was when I stopped getting XP from them, same as the Knights) and their mind-affecting ability is a self-centered AOE that has a save instead of a touch-attack bolt.
Switching their confusion bolt for a confusion howl ability would make them more in line with their PnP version, make their effects able to be defended against in more than one way (as opposed to clarity or you're basically unprotected) while still leaving it dangerous, and generally making them more interesting to fight against IMO since there would be more uncertainty.
I'd probably still up their XP reward though, but as I said, there's so few the difference isn't that big.
(also probably give them automatic quicken spell and epic combat casting for their invisibility if they don't have those already so they can spend more of their time invisible like their PnP counterparts)