There isn't much humor in this game, but I have to assume this boss's post-death face is intentionally funny. The other vamps don't do this. Or at least the normal ones >>538916373 >>538916854 don't.
I'm not sure why his mouth graphics are fucky, but it's not a Linux issue, because a screenshot on the game's Fandom wiki shows the same visual glitch.
By the way, almost all of the text of that wiki page
>https://nosferatuthewrathofmalachi.fandom.com/wiki/Desmodaui
is lifted verbatim from this FAQ/walkthrough
>https://gamefaqs.gamespot.com/pc/917976-nosferatu-the-wrath-of-malachi/faqs/37705
(which starts with "please don't steal my work" but they did it anyway).
I knew Fandom was shit, but damn.
To some wiki editor's credit, however, the one piece of information I needed also happens to be the one paragraph NOT blatantly stolen from that walkthrough. I had actually tried the walkthrough first, didn't find it, tried the wiki page, saw it was an exact copy, and almost gave up... but for some reason I checked the bottom of the page, and in the last paragraph:
>There is a bug where if you kill Desmodaui too quickly, he fails to appear in his coffin afterwards (it will be empty and already open).
Basically, holy water one-shots the boss on easy/medium, and doing that too quickly can break the game. This >>538925261 was actually more than slow enough, but I didn't save the game after recording that video, so I was repeating the fight and killed him immediately. Then I ran around for 20 minutes wondering what obscure shit I needed to do in order to have him appear in his coffin, not knowing I had soft-locked.