Belphegor doesn't seem like the type of group that would tone it down just so its art will be accessible for everyone. For instance, the video for "Black Winged Torment" off the band's currently-out album Conjuring The Dead. The video isn't NSFW because there's lots of nudity, people getting ripped in half or anything like that. No- this video is NSFW because it's the type of shit that you see in your own nightmares.
Maybe it's the way it's filmed or just the excessively well-done makeup. I'm not really sure what exactly it is about this that creeps me out, but you'll get what I mean… yet it's so damn good I can't stop watching.