I am wondering if anything would accompany an intellect devourer.  I am having a colony of mind flayer warring against a drow empire in the Underdark of my homebrew world.  And to me it would make sense to have something with the intellect devourer as it goes to infiltrate the drow.  What all would accompany the creature?  This would be more for a random encounter.  And allow for a little more for world building.

Pretty much any critter could be a scout if you have the Intellect Devourer piloting them. It stalks a creature, devour's their intellect and then uses Body Thief to take them over, maybe have a displacer beast or a grell or grick with them, and see if all those waving tentacles weird the party out a little.

I would guess that an intellect devourer would be a shadowy "secret scout" amongst a small scouting band of creatures enslaved by the mind flayers, probably troglodytes or grimlocks or some other collection of monsters. Basically, the larger scouting party would be the distraction that a counter-party of some kind would encounter, and while the fighting is going on, the intellect devourer would attempt, covertly, to get inside the head of an enemy, so that after the battle, they can sneak back into rival territory with the assumed "victors."