Yeah, I just always blank on that bit about Multiattack.
So, anyway, what do you think about those feat suggestions?
Looking good. Org, alignment, and treasure all look ok to me and can be de-redded (how many d's should there be in that new word?).
Advancement could be maybe 9-16 HD and 17-32HD? What do you think?
Odd, I must have looked at the master scorpion's org. In any case, I agree with the suggested org and am fine with switching the advancement as you propose.
I guess we could do the tactics before worrying about CR, but I think I'd peg them at about CR 8. They're better than an erinyes in some ways but worse in others.
It's definitely a worse than the bone devil defensively and is roughly equal offensively (less damage output but stronger poison). The mind flayer does seem a bit weaker than the monarch scorpion, but the mind blast is stronger in the sense that the stunning lasts longer. I will certainly agree that it's considerably better than a Huge monstrous scorpion.
Well, it seems to me to be between CR 8 and 9. Given how imprecise these things are, I don't think it matters much either way. CR 9 will work.
Guess it's CR 8! You're also right about the range for the mind flayer. I didn't even look at that comparison.
Tactics: Uses psychic blast first as a ranged attack, then enters melee? Judicious use of psionics?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.