I can't wait for werewolves to join my vamps. I think a werewolf rank system similar to our vampire one could work well i.e. as you earn ranks/points, different strengths and weaknesses become available.
Some possible strengths (in wolf form) could be super strength and stamina or speed, the ability to pass on the werewolf 'curse' with a bite, and of course an enhanced sense of smell to help them find collectables and other hidden treasures. I would suggest this includes smelling emotions too, but all sims seem to have empathy anyway. They should live longer and of course be able to join packs and climb different ranks. Maybe the leader/alpha can control the others and they can all howl to call other werewolves near and scare other sims. Perhaps they have to earn the ability to change into wolf form outside of the full moon or even prevent it happening? Or you can choose a lone wolf perk where you don't need to socialise (but perhaps can't be in a pack)? I don't know. There's lots of possibilities and I'm sure others will have more and far better ideas.
As for weaknesses, there's silver of course, which could deplete their energy or make them tense, similar to garlic for vampires. Maybe a ravenous wolf has to eat a lot of meat or they lose control and bite other sims. Maybe some get cranky and have less control of their emotions/anger near the full moon. Maybe some are forced to change into wolf form during the full moon whether they like it or not, and in wolf form they have less control of themselves, get hungry faster, scare other sims, and/or are unable to talk. Or maybe some are just a little too hairy, growl and/or sniff other sims even in their normal form and it puts other sims off, or maybe they always stink like wet dog lol, particularly if you're a vampire.
