For the record, I began my Subnautica Nightmare series and zombie textures long before The Red Plague was even a thing, but since the release of TRP I realize these textures go really well with TRP so I'm releasing what I have so far and will be updating this mod more as time goes by to include every biome in the game. This mod changes up the textures of most flora/fauna (Includes the Zombie Reaper) in the safe shallows, and adds some creepy structure and terrain edits as well as adding a few additional Leviathan's nearby to make the safe shallows, NOT SO SAFE! This mod now comes with a dark shader, custom creatures, tornados (or water spouts if you wanna get technical), and a bunch of updated biomes! It should be compatible still with The Red Plague for a truly terrifying experience. Using Lee23's biomefog command code, I was able to make bloody water! Only issue is that Bloody Water is not compatible with Spooky Subnautica, you will get really weird red effects so choose one or the other. You will also need the Epic Weather Mod for the water to look right, and yes it will be cloudy and rainy the entire time, no normal sunshiny days.
Warning: Tornados do add a lot of particles to the game. If you're computer is ancient then they will drop your fps if you get too close to them.
As a side note I will be releasing a separate Tornado Mod, Peeper Leviathan, and Crustacean Infestation as separate mods as well. These are just the Nightmare versions of these mods.
Update: Fixed the peeper leviathan so I re-added it's spawns in but still working on it's LOD issues.
 
Future Ideas: I plan to build a maze of teleporters that will lead to either rewards or disaster. We will even have spatial rifts that will lead to a void dimension full of horrors. I also have ideas on how to make a whirlpool that will suck the player down into the void. Hallucinations, creepy sounds, and storyline will all be added at some point so stay tuned for updates!

A COMPLETE STEP BY STEP TUTORIAL HOW TO MOD SUBNAUTICA AND INSTALL THIS MOD: https://youtu.be/qQtwqYRNlLA (This video is slightly out of date! Silence was removed, so no ECC Library required. And now be sure to download The LATEST TERRAIN PATCHER, TERRAIN EXTENDER IS NO LONGER REQUIRED! Epic Weather is now a requirement, and the Nightmare folder goes into the plugins folder like any other mod.)

To get the full details regarding the storyline of this mod, and if you have not seen my Subnautica Nightmare story series, parts 1 and 2, please give them a view and Subscribe to my Youtube Channel: @leviathankraken
Part 1: https://youtu.be/TrVyoYL9_H0
Part 2: https://youtu.be/iWPwfeuFZkc

To Install you will need Bepinex, Nautilus, Epic Structure Loader, Texture Replacer Mod, Terrain Patcher(latest version), and Epic Weather Mod. 

Each folder in the zip file is labeled to help you know where to place everything. Simply drag each folder's contents to their corresponding folder in your game's directory do not drag the entire folder. Nightmare folder goes into plugins. You can delete some of the leviathan spawn structure files if the challenge is too difficult.

For further help installing join my discord: https://discord.gg/DgQPWtyJFD
Please report any issues or glitched textures to me.
Known bugs:
1. I have seen a tornado spawn sideways but I 'think' I fixed it. Please let me know if any do this again. Also I'm not sure how the tornado will interact with other mods so please keep me informed of any of weird glitches.
2. I know the water surface looks like a blue sky when you look up from underneath, and I'm still trying to figure out how to fix that. 
3. I have also seen some of my devil reapers get relocated somehow, and again, I 'think' I fixed that as well but please let me know if they start relocating, If so, just delete the devilreapers structure file.