Never really thought about it before. Looking at it now, it seems like one of those old paintings depicting Hell with a lot of naked/dead people. And a bloody looking Mary because Dracula is just that anti-establishment.
At her feet though, between what looks like demon horns... I know I'm really, really reaching but it looks like ovaries, like one of those old pen and ink drawings from an anatomy class. Maybe an allusion to what caused him to become Dracula in the first place (an innocent woman being killed)?
Iunno. Fun to speculate, though. Looking at the stuff outside what's obviously Mary is kind of like one of those ink blot tests.