And for humans, the expensive Castle – Archangels cost 30 gems + a ton of gold, overall. And they don't heal very well.
Respect to cavalry, but that bonus, if I'm not mistaken, also exists for Death Knights... (if they don't mess up).
Archangels don't heal, they resurrect. One Archangel can resurrect 100 health. Archangels cost 20,000 and there are only 10 of them.
Human horses get a +5% damage bonus for each cell they move. Necromancer horses have a 20% chance to curse and a 20% chance to deal double damage.