I loved the 5e mystic the mechanics need more time, but the thematics were pure gold to me, it was like seeing something that always fit you.
Also I like monk I just do.
if they are going by medieval Europe logic racism would look unrecognisable as what you looked like was of far less relivant than being of the right faith or having sufficient gold.
My point is more the pot of things to draw from is massive and deeply strange. Mix Sufficient things together, and one very good idea is likely to emerge from the creative primordial muck.
Those are all very brutish; whatever the end result is would be much more gaunt by nature, it is all brain rather than brawn.
Regardless, the Doom Cosmic Baron fits the above fairly well
I have seen Eldritch ghosts in media, for example, this guy
Given it would be to psionics what elves are...
My point is, I want a shared baseline, which I can't do.
It is wotc job to make people want to play their products and mere stat block and character archtype is not a finished product and unlike dwarves and elves with other fantasy world to do the heavy lifting goliaths are theirs alone thus...
Dolgaunt seems a bad place to start, as well as cenobites, who are technically a monastic order.
Now, there are ways to work on a biomechanical look
But you need more than that and more than just tentacles.
Also we do really lack something properly monstrous looking to play everything has...