Mutations: skin cancer/brain cancer/intestinal cancer/eye cancer/etc.
They lower your stats, decrease health, cause regeneration penalty (can become negative) and spontaneously mutate into stronger versions.
And variants that metastasize onto other body parts.
-4 str for female characters. For “realism”, of course.
Irradiated zombie scientists who turn into atomic zombie hulks when angry. Atomic zombie hulks are faster hulks with leap ability.
Ability to pacify a zombie by showing it something from its former life, making it regain some mental functions and bringing it to tears.
Sentient zombie NPCs