Tielby
Prince
IIRC, you lose the promotions that automatically gain XP (the one that any adept/mage has, but I think the hero loses the Hero promotion as well) and you become vulnerable to the Destroy Undead spell, but like any Undead, you are then immune to some other spells, including some beneficial ones like Haste. Since those hero units already have Channeling III, I consider it a waste of a perfectly good national unit slot.What happens if a hero mage unit (Hemmah, Govannon, etc.) casts Lichdome?
Actually, now I can't remember if liches are national units, i.e. limited to 4.