This black sleeping dragon is very fond of gold.
Most of the time, Beresad is busy sleeping and guarding his hoard of treasure. For a (reasonable) price of 100 Gold, Beresad can be paid to wake up and use his Conflagration ability, which sets the whole path on fire with Beresad's green fire breath.
In the Heroic Challenge, Beresad is apparently busy with something else, and is not available. His lair is temporarily occupied by a large green lizard which strongly resembles Yoshi from the Mario series - it's unknown what (grim) fate befalls this lizard when Beresad returns in the Iron Challenge.
Immediately after getting paid, Beresad will take flight and begin to breathe green fire on the whole level: he starts by burning the path on the southeastern 'island', then flies to the southwestern island and sets the path from the Sorcerer's Stone to the western exit on fire, then continues to breathe fire on the path from the teleporter to the southern entrance, and finally lights up the northern island before returning to his lair to sleep.
100 gold is a cheap price for an attack that deal True Damage across the map, so save in advanced to use it when the area is filled when enemies. It could save you a lot of firepower and potentially regret in the future. Young Beresad is particularly useful to the point of being critically required in the Iron Challenge where his attack is exeedingly powerful against the swarms of Spiderbrood, Sword Spiders, and Cloud Stalkers that come in the challenge.
D&D Have Beresad and Ashbite defeat 100 enemies.
The mature dragon Beresad would be encountered many years later by the human and dwarf allies of the elves during their campaign against Lord Malagar, which leads them near his new lair in the underground caverns - only this time, he is their enemy, possibly after having been bribed by Lord Malagar's Saurian minions.