Continuing my run lately of converting stupidly potent monsters to 5e, I present the "Brain Collector"; a warped nightmare that has actually been around since D&D was in boxes. The version I converted was the 3.0 Epic Level Handbook's one - partly because the art is so good in that one, and partly because its potency is sick.
In my games, these things are referred to by the few that know of them as the "Handmaiden's of Xix", an allusion to their distorted and insane form. In fact, the God of madness rarely makes use of these things, as he finds them too strong willed and hard to control.
Anyway, if your group have really pissed you off, here is the monster to let them know. Combining Brains (not its own) and brawn - the Neh-Thalggu!
Why don't you find me attractive? Is it my lazy eye? It is isn't it. It's my lazy eye...