The most useful monster.

Vampires are the strongest creatures of level 3.

No, that's not true. No one takes them on in a one-on-one fight; what's the point of having attack bonuses then? And in battles with equal numbers, a vampire clearly loses to a Djinn or a Crusader (if the vampire can't fly and it's just a wall-to-wall fight).

About battles against undead, mechanics, and elementals.
It's quite weak against them; you need to attack very carefully because +1 to Dracosh means few hit points, and therefore they die quite quickly...

The strongest and most useful hero.

I strongly disagree. First of all, there is no "strongest" hero – give me an army of equal strength and tactics instead of nature magic, and we'll see who is stronger :) ...
Well, I just don't like banal phrases, but that's what makes the 4th game good: each race is unique, and so is each hero, and each skill is irreplaceable. :)

Because if we're going to discuss something in this thread, let's do it without the prefix "the most."