This was a Gearbox Lighting Team collaboration as every one of us dogpiled on it due to rotating vacations and downtime recovering from shipping the main title. Everybody sliced off a chunk and worked on it:
Anngelica Parent did the lead-up to the graveyard:
https://www.artstation.com/anngelicaparent
Piet Braun did the graveyard and outside courtyard:
https://www.artstation.com/pietb
Jean-Pierre Arias did the true heavy lifting of the interior and the boss fight arena and was responsible for the level as a whole:
https://www.artstation.com/jparias
I did the blood cave as depicted here and the time of day. When the level was handed off to us the time of day was a saturated, fluorescent green which was fun in a nerf sort of way but Halloween is a big deal to the Gearbox Lighting Team so I went with a more mature color palette that sees the sky light be a sickly green and the fog provide a dusky pink contrast.
Dave Avery did the level art:
https://www.artstation.com/davery