The most USELESS monster.

I agree about the leprechauns. I also think that elves and hives are somewhat useless when playing against Haven or a hero who knows Haven magic. One spell of "Forgetfulness," and the elves become incredibly weak fighters, and the hives become very slow – they won't even be able to crawl to the enemy. Of course, the "Forgetfulness" effect is neutralized by anti-magic. But you also need to consider how speed and/or morale will affect the druid or mage.