Wearing its Lovecraftian inspirations on its sleeve, I feel like Bloodborne just didn't have a lot of the non-fleshy or non-combatable monsters from the author (and his descendents') writings. Oedon comes to mind, but the list kind of ends there. So, personally, I'd find monsters or entities that are less about flesh and blood and screaming interesting - think the Color out of Space, for instance. Or perhaps creatures that are not obviously and directly hostile, and more part of the environment (like those cosmic babies in upper cathedral ward). Not that I have any problem with tentacly werewolves and their screams (I can't get enough of Amelia's screaming...) but it'd make a nice change of pace to have more of the "weird" in there. Something that would make even a high-level hunter go "what good are my super powers now? I can't fight radiation with an axe!"