This is actually a screenshot composition in ULTRA settings and 4K resolution, I’ve used a Cheat Enginee table to manipulate FOV and camera cords, the snapshot via nvidea Share (ShadowPlay) or the same Cheat Engine and retouched in Lightroom for this dramatic Black and White effect.
I’m surprised that Dark Souls 3 have been out for almost 2 months now, and still if you try to look for HD screenshot of each boss, there’s almost nothing, neither to say, nothing HD.