Say 'vampire,' 'werewolf,' or 'zombie' and anyone with a television knows you are talking about a very specific kind of monster. This isn't a bad thing. Despite the lectures I've heard from agents and publishers, if someone manages to find an interesting spin on these creatures, people will read or watch it. That said, there are thousands of creatures to draw from. Why not mix it up a little?
While I work through The Hunted series, I try to throw in mythology I don't hear on a regular basis. The heroine of my series is a vampire (kind of), and I wanted to avoid the werewolf-vampire love triangle. I adore werewolves, but it wasn't right for the series. I needed a fierce warrior, and a timely reminder of Vikings flashed on the History Channel in my living room. Why not a Berserker?
In the world of paranormal writing, reality is just the starting point. Options are plentiful. The berserker could be a shapeshifter, adopt some of the animal features, or maintain human features with limitless strength. The creature could fight with skill or it could adopt additional powers more fantastic than legend. I chose to use the myth about iron and use it as the catalyst that changed the berserker from human to other. I exaggerated fire and gave them the power to wield lightning. Instead of having the berserker shift fully into a bear, I chose to have the features distort in the flashes of lightning.
The key to writing a paranormal creature is consistency. Develop a lore that works with your world and stick with it. I use Scrivener to help keep track of both characters and the mythology built into my world so I don't contradict the biology or magical constraints that have been established. If you're writing about a common creature, you can choose which features to keep and which to throw out. If you find a rare creature, there isn't a precedence to compete with, and that can be freeing.
Is there a rare creature you wish was featured more often in paranormal books? Do you see something in paranormal creatures you wish wasn't featured as often?