Ohh, let's see...
First off, a Focus meter above the needs. Focus would be gathered by your Sim through various means, eating specific herbs or meditating. Focus would keep you in control of your Werewolf when he/she transforms. Otherwise, you might risk your family members instead of that Vampire you planned to hunt off your property.
Various stages of your Werewolf - the pup (only for children) lesser, common, greater and Alpha Werewolf. The more you climb the stages, the more focus you need to build to control your wolf, but in return, your predator gains longer life and wastes less and less energy during those wild nights. An Alpha Werewolf can assume dominance other Werewolves that shows up in the neighbourhood, and have them hunt whomever it pleases, even invite it to join the Werewolf's "pack", be they human or other Werewolves. Werewolves would have the ability to woohoo other Werewolves in bushes or in Sulanis waterfall.
Take care with your Werewolf! For all your aquired focus, the more you let it go wild, the bigger the risk of the Werewolf going berserk and doing as it pleases until it reverts back to human.
The Werewolf, controlled or no, will have the ability to fight other Werewolves and Vampires.
A new type of door. The reinforced door. Don't trust yourself to not hurt other Sims or maybe you don't want to? The reinforced door will keep your Werewolf locked up for the night, although it might need some repairs the morning after. And your Sims might have a sleepless night listening to the howls of a berserking Werewolf trashing its room (that new fear emotion will be a welcome addition if they include Werewolves). A small price for safety?
What kind of Werewolf will you be? The one who loses control everytime and is the curse of the neighbourhood? The one who controls and embrace its inner animal? Or the calm one, who controls it and stays indoors, refusing to go out and lose themselves to the beast within?
I don't know much about Werewolf abilities, so I leave it for now.
