Am I allowed to copyright this name?

First of all, you are referring to a trademark, not a copyright. Second, you cannot obtain a trademark on a name if someone else is already using that name in such a way that your use would cause confusion in the marketplace. Certainly, if someone else already has a registered trademark and your use does not pre-date theirs, the answer to your question is no. If your use does pre-date theirs, the answer may be yes.

No one can register copyright on a word or title, such as Mafia or Mafia/Werewolf. However, you may be able to register trademark on a card game named Mafia/Werewolf. I work registering trademarks and my very strong advice is to have a lawyer do it. Do not use do-it-yourself website because my observation is that nearly all of those registrations are done incorrectly and fail. Trademark law is very complex. If you succeed at getting a registered trademark for your card game, this is very valuable.

Certain words and phrases can not be copyrighted. These include proper names, titles, and short phrases. Your game itself may qualify for copyright but not the name of it. If the word you want to use is a registered trademark, you probably can't use it.