For a moment, I thought this was an in-game screenshot, but then I clicked the link and saw that it isn't. Wonderful work on the detail there.
By the way, I found this boss sort of scary when I first played it. The way his face looks sort of resembles a mask like No-Face's mask in Spirited Away, which is also rather creepy, and then in Phase 2, it changes into a more menacing-looking version of it with a wider mouth and Devil-like horns. Oh my!