The most useful monster.

it's more like a ranking of powerful creatures than useful ones (or cool combat skills))))
vampires are strong, but that's all... bone dragons with vampirism are much more useful, if you consider that aspect)))
because angels with resurrection are more useful (when a hero-mage is killed in the final battle, and he didn't have time to drink a healing potion a second time) or cyclops that attack everyone)) and those who cast slow spells and other spells)