A werewolf is a human that changes into a wolf like creature during a fool moon, they return to human form before the next day and often have no memory of events that happened during the night. While in a wolf like state they kill livestock or infect other humans through their bite or scratch causing those people to also become capable of turning into werewolves. A Lycan is a type of werewolf popularized in the Underworld movies, they have the ability to transform into a werewolf at will, unlike traditional werewolves that only change during a full moon.
Since werewolves are humans that transform into wolves it is possible to wear a partial werewolf costume that feature just the hands of a werewolf then add lots of fake beard hair to your face. Even an extreme werewolf costume like the one picture below still allows you to wear normal clothes for your bottom half since you are part human and part wolf.
A Werewolf Costume
Extreme Werewolf Costume
A Werewolf Costume For Halloween
The lack of memory that some werewolves have during their transformation fits well with wild parties where you might drink too much and suffer from real life memory loss of the events during the evening. For a less threatening option than a traditional werewolf you can choose to wear a costume like that from the hit 1985 movie Teen Wolf. For couples, a great option is to mix a werewolf costume with a little red riding hood costume, although the wolf in the classic fairy tale was not a werewolf they are still a perfect fit.
Teen Wolf Costume
A Werewolf Costume For Children