The third of the trinity; Opiate, brings "photorealism" to the table. Again focused on the beautiful and the horrific, but due to its realism the more gruesome aspects can really punch you in the face.

Opiate v5

(Personal note in version details). And straight into the:

Bro Science

With the last version I found it a bit resistant to the more horror aspects of what I enjoy making so...

Step1: Smooth step Opiate v4 over Dread v4 producing several models of varying capabilities.

Step2: Mix these models and vanilla Opiate v4 and Opiate v2 until happy with the results.

That's it. All the generation suggestions below still hold true with the addition of using DPM++ 3M SDE Exponential, at times. All suggested samplers are viable. (If you're new to all this note that the usage suggestions are just that. Suggestions. As you get deeper into this rabbit hole you'll notice that things are actually far more malleable than they at first seem, so, enjoy the ride).

Usage Tips:

Samplers:

DPM++ 3M SDE Karras and DPM++ 2M Karras: General purpose workhorseseses, I like to use it for pretty much everything.

Cfg:

4: Great for pretty much everything but especially photographic styles. (My favorite)
5 -> 7: Great for pretty much everything, as it goes higher it's use for photography diminishes but is as, if not more, useful for artistic styles.
8: Great for some art styles but will burn photographic generations to a cinder.
9 and above: Yo crazy.

Steps: 30 to the limits of your patients. I never really use more than 50 and find that above that it's a case of diminishing returns.

HiResFix:

(I consider HiResFix a must for all of my SD 1.5 models. They are not intended to be used without it).

4xUltraSharp
Denoising Strength: 3 to 5
Steps: I tend to use around 50% of original step count.
Upscale: 2

Clipskip 1 until 4 give interesting results; for characters it becomes more unstable the higher you go, for monsters it seems to get better. After 5 things get shaky but when it hits it does so in a more artistic manner.

(A quick word on negative prompts: if you are aiming at horror many of the things you would normally prompt against are the very things you want to have eg: deformed, mutated, ugly etc. Just be aware if you're making your own beasties maybe just start with quality related negatives, and build it up from there. Also one thing I noticed when making the demon chick is if you prompt against :- male, man, masculine - too harshly it drastically effects the output in a negative way. I'd guess there are many more images out there of male demons, but as you watch it generate the body type will change to the feminine. So... with horror stuff, be cautious with the negatives.)

Anyway I really hope you enjoy exploring Opiate's murky depths.