Nasty trick with Planar Binding spells!

[VirgilCaine]

I suppose however that's it's entirely up to the DM if a simple planar binding spell is able to reach outside of the normal multiverse and wrench something to your specifications from some alien, antithetical reality.

Personally I'd do one of three things: 1) if they didn't have any idea in-character what pseudonatural things were or where they might come from, they couldn't cast the spell, 2) if they knew in-character about them and such, the spell would still fail, 3) or depending on my mood it might work, but not in the intended way, and they'd probably end up pulling an Alhazhad in the sense of being devoured by invisible monsters in public.

Al-Haz-red. Abdul Alhazred. That was the man's name.

Personally, because this brings D&D into the realm of CoC, I'd let the spell work...but whether it brought what the caster wanted or whether the creature is bound is another factor entirely.

 

[lukelightning]

I'd be more concerned about what a pseudonatural creature would ask for in return for service.

What? Payment? Bah! That reeks of those suck-up clerics brown-nosing with their outsider "allies." Things I call better do what I say or I'll obliterate them! I have a +6 modifier to my charisma check; a pseudonatural troll has a charisma check modifier of -2. RAW that's all that is needed; rewards give a possible bonus to this check but lack of reward gives no penalty.

Granted, in my experience DMs make the planar binding spells into "screw the player" spells, rather than a high level spell that requires extra preparation, time, and other spells (magic circle vs. alignment and probably dimensional anchor). You call a demon? Surprise, it's a demon lord instead of a babau and it eats your head. You call an archon? Surprise, a solar shows up and puts you in magic paladin jail.