Simple, in setting enemies for a 'zombie' style game:
Insect spirits
Shedim
CFD
Shadow spirits
People assume insect spirits are stupid. They are not, they are highly intelligent! Able to stay hidden and blend in with society. Well, the trueforms anyways. And a colony of Ant spirits get discovered under some city, come bursting out and attacking. (The CZ all over again)
Shedim need uninhabited bodies to stay on this plane, and like it or not, there are plenty of corpses all over the place in forgotton graveyards all around the world. A colony of shedim suddenly springing up is not unheard of.
Shadow Spirits feed off of negative emotions, and have powers to instill and amp-up these negative emotions in others.... a few shadow spirits of Rage, infecting a handful of people with homicidal rage can be.... interesting.....