I finally finished the game! So good. In the post-credits scene, my game suddenly got very laggy as opposed to running smoothly during the main game. Once I got to the top of the stairs, I was greeted by this:
I can't speak to the lag (not the programmer typing this particular message, I'll send them over) but the skull floating definitely isn't a glitch, that's meant to be there. The lag isn't, though.