Throwing some random stuff out there regarding Undead Rising, if we/you were to create an undead Faction:
Special Units (the other factions get Spiders, Demons and stuff after all):
- Vampire (Life Steal ability -Enemy Health +Own Health)
- Zombies (Lower Action Points but Regen to compensate?)
- Grim Reaper ("Touch of Death" with insta kill ability would be overpowered I guess? But so are Dragons and Demons! 
)
Race Uniqueness:
- no need for Food? Other resource / tech / way used to level up towns?
- in general (when it gets implemented) resistance against piercing/slashing weapons but weakness against blunt damage? These unprotected bones shatter easier after all
- Living, "good" NPCs demand more Money to join / won't join at all?
- Enemy looses more morale or gets a general handicap when facing an undead faction in Tactical Battle?
- Healing spells damage undead units
Special Spell Book:
- Vampiric Touch (Life Steal ability -Enemy Health +Own Health)
- Summon dead (like Raven X already hinted at a spell to Summon Skeleton Units)
- Some Fear spell that makes the target Unit loose their turn
- A Spell that lets you control an enemy unit for a turn ("Hypnotic Gaze"?)
