The gray glutton prefers to spend its time posing threateningly on the perfectly clean skulls of its dead foes, as 2 int monsters are of course wont to do.
Snark aside, the Glutton has a semi-promising chassis. Huge size is neat, and 27 strength is hardly bad. Constitution, wisdom, and surprisingly charisma all get reasonable bonuses too. Although all this is at the cost of 9 RHD, it's magical beast RHD which makes it a bit more manageable.
Natural weapons are a 2d8 bite and two 2d6 claws. Based on claw shape I think it's fair to argue they can wield weapons, but don't expect any DM to echo that sentiment. Scent is hardly worth mentioning, PR 20 is probably a net positive, and finally there's their main ability: Null Psionic Exhalation.
Some naive fools, like me, might have read that name and expected something similar to Null Psionic Field. Getting what amounts to an AMF at ECL 9, is actually kind of a Big Deal, as even wizards don't get it until level 11. Of course, it couldn't quite be that good.
Instead, Null Psionic Exhalation is a free action, usable every 4 rounds, that spreads poison. Said poison's sole effect is to remove a few power points from its victims, and in a game where the average psion foe will have over seventy power points I doubt 1d4 will make much of an impact. The effect doesn't even count as a breath weapon, so it can't be exploited that way either.
While the gray glutton offers the appealing combination of 27 strength, huge size, and thumbs, its lack of real other abilities makes me slightly skeptical as to how useful it'll be in a real game. That said, for now I'll go ahead and assign it +0. I'm half expecting it to drop to -0 though.