Achaierai
It's got 6 RHD, which already kinda sucks. These are outsider levels...which are probably among the best racial HDs...still not good, but at least not among the worst. Of course, all of these monsters are going to be hampered by RHDs, so wouldn't it be a better effort to try and represent the monsters, nix those?
So, I'll assume that you get ability and feat adjustments from RHD as normal HD, and that it assigned +2 to strength. I am also assuming that the base abilities of the monster entry is equivalent is the "average" specimen, as 10 is an average human.
Abilities: +7 Str, +3 Dex, +4 Con, +1 Int, +4 Wis, +6 Cha.
OK that's...rather radical.
Natural Attacks: 2 claws (2d6 damage), 1 bite (4d6 damage?!). So 8d6, given a full attack, 4d6 on standard action.
That's fairly significant, equivalent to a 4th level caster on a standard action...if they were blasting...with the restriction of melee...but let's not talk about that.
Speed: 50ft, or 10 squares.
That's noticeable in some campaigns.
Sight: Darkvision 60 ft.
I won't factor it in, just noting.
Spell Resistance: 19.
Equivalent to an 8th level drow. Doesn't continue to scale though. Also I don't think I've had anyone play Drow for anything but RP reasons.
Size: Large...but based on the Advancement, we could easily say Medium, since we are taking away the HD. So, let's just say Medium.
Special: Weapons and natural attacks count as Lawful and Evil for purposes of damage reduction
Black Cloud: 3/day, targets in 10 ft of Achaierai take 2d6 damage.
There's a bit about insanity as cast by a 16th level caster, but that's not really going to come up in an Adventurer's life. It doesn't mention a cast time. I assume it has one though, so none too significant.
Incapacities: The monster entry says it can wield weapons. Unlikely to be firearms, or even reasonably a bow, though, because of how the claw works. One could argue for it not being able to cast, because of not having hands, nor anything that specifically lifts that requirement, like Dragons do.
LA: Probably a +3, and maybe restrict it from play until the party's level 6? As far as martial characters go, it's fairly radical, mostly due to its stat adjustments. Even the odd Bard or Sorcerer (assuming they can cast), might pick it in a...rather low OP setting. The spell resistance is highly valued when concerning most LA, as well. Natural attacks are also pretty darn good, even without need for optimization, and add a lot of early game power.
LA buy off would allow you to negate +3 by level 9, which seems decent. Level 16 is far too long though. However, its early game strength can be overwhelming, and not something the rest of the party can keep up with.