https://www.kaydora.com/
It was a tough call for this one. The majority of this list could be filled with Bloodborne enemies.

The giant brain of Mensis, the amalgamated mess that is the One Reborn, https://www.kaydora.com/ even the spindly Amygdala or many-eyed Rom, the Vacuous Spider. Bleh.

Instead, I went for the Winter Lanterns.

Whilst the others are gross in their own right, there's something just so inherently disgusting about a mass of eyes and brain on a spindly, doll-dressed body.

But it's when they lock eyes onto you, that's the bit that makes me go all squeamish. Those many eyes widening, the unfolding arms from wherever they were hidden, right before it latches on and munches you with some kind of mouth-like orifice.

That they cause Frenzy build up when they see you is bad enough, as it can ramp up and take a massive chunk of health before they grab you. If you're luck is that bad, the combination of both take you completely out if you're not prepared.

From a battle perspective, avoid them. From an "Oh god, my sanity and stomach" perspective, definitely avoid them.
https://www.kaydora.com/