Nigon is the second underground race.

Behemoth is a monster from the Bible, some kind of demonic creature. That's why Bulgakov named the cat Behemoth, as a demonic creation. I think it's clear to everyone what a behemoth is doing in Heroes 3. So, regarding the hero's appearance, you could make it so that he rides on some creature from his castle, but that wouldn't be interesting, as many people are only interested in seeing a creature of a certain level sooner and try to build it as quickly as possible. But here, the hero is already riding it at the beginning of the battle – there's no competitive interest. I think the hero should be made to be on foot – a figure in a dark brown (or some other dark color) cloak with a hood and a staff in his hands, attacking by standing still and throwing some kind of nasty thing at the opponent.