YouTuber and modder Limit Breakers has replaced every single texture in Dark Souls 3 with a kitschy pattern depicting a crab atop a black background.
From the armour to the landscape to the enemies, it's all crab as far as the eye can see. Near the end of the video we even see a giant enemy crab made out of crab.
Even the HUD, when it's enabled, is made of crab, making your selected items completely inscrutable.
Limit Breaker uses the iGP11 mod by S17L that lets you replace textures in-game. To make your own nonsensical nightmare fuel, you can grab iGP11 on NexusMods.