Intellect devourer

Intellect devourers are a species of aberration who look like brains with legs.

Intellect devourers are like neothelids in the sense that they're not a huge deal in D&D but got a huge upgrade in Pathfinder. IDs and neothelids both get overshadowed by D&D's mind flayers, but because mind flayers are WOTC's IP, Paizo made IDs and neothelids much bigger deals in Pathfinder.

IDs in PF are not the servants of mind flayers but rather are their own bosses. They have their own empire in the Grimdark, and have fought many wars against other subterranean peoples.