Buff zombies, to make them more of a threat. Import FIQHack zombification (a zombie bite will place you 90-100 turns away from turning into a zombie, each additional bite decreases the timer by around 10 turns, but it will go away by itself if the timer doesn’t dip below 40); boost their difficulty, but keep their HD low; allow them to revive themselves less frequently than trolls, but also revive themselves whenever another zombie steps over their corpse.