So I'm a Souls modding tool developer and I've worked closely with Stayd (the author of this mod) on developing the tools needed to make this mod possible, so I can give an overview on what this mod is doing and how it works.
At the core of this mod is the upgraded shaders. DS2 SOTFS is ultimately based on a PS3 era game and most of the shaders and post-processing is very low quality compared to PS4 counterparts. By reverse engineering and decompiling the game's shaders, Stayd was able to rewrite many of the effects to be of much higher quality. Everything from material shading, antialiasing, ambient occlusion, bloom, skin shading, and more was upgraded with higher quality versions.
The mod also adjusts the game's "filter parameters" which control things like the sunlight, ambient light levels, color grading, fog, and other things. It's kinda like tweaking a reshade but since it's in engine, you have much more control over the look and can tweak it on an area basis. Stayd is also able to edit per-object rendering parameters to make many more objects shadow casters and increase the number of point lights that can cast shadows at the same time, making the game look much less flat.
The most ambitious part of the mod is the map and light edits. With a Unity-based map editor I created, Stayd is able to edit the placement of dynamic lights and map objects. In many maps, Stayd added many more dynamic lights and fixed many cases in the game where the lights don't match what you see in the environment (i.e. windows not being a big light source, tunnels being super bright without any kind of light source, torches added where they make sense, more minor incandescent objects casting lights, etc). He's also taken to doing map edits that aren't directly related to lights such as adding props and clutter to many of the empty rooms in the game and trying to enhance the visual storytelling in the game (making more of the areas seem to have an actual purpose beyond being a gameplay setpiece). Outdoor environments are also edited to have much more dense foliage and things like trees, rocks, bushes, etc are added.
He's also been working on other changes that may be more controversial such as redoing enemy placement and making lore/item description changes where he may see fit, but he plans to release those changes as an optional part of the mod.
