The main character is a vampire hunter, who was banished by his/her village to walk the swamps, after s/he was framed for the murder of the Captain of the guard. S/He encounters the cultists first, who attempt to capture and kill him/her. A vampire attacks, and s/he kills it, so the cultists worship him/her as if s/he had the blood of a werewolf, to slay a vampire. Throughout the story, the hero can change alignment with all the factions, killing several vampires or undead will make the villagers like him/her more, and werebeasts will eventually leave him/her alone, depending on their aggressiveness.
The main character does not have any magic, however, and only starts with a crossbow and a dagger. The only form of magic is from killing witches, who hold wands. The witches are powerful mini-bosses, and the wands are limited use, but very powerful.
The main goal of the main character is to slay the vampire baron, and all his kinsmen. The baron is unassailable as long as all the other vampires live, and the witches need to be killed to obtain a certain object from all of them to weaken the barriers to his room. The castle could be thousands of room large, and the swamp could be as big as Skyrim.
I could write a book on it, because I think about different ideas it could work with whenever I'm bored. But I'd probably explode the forums if I tried that...
