Yk'Lagor the Thunderous

Yk'Lagor the Thunderous is the final Dungeoneering boss monster encountered on the occult floors (36 to 47) of Daemonheim. He is classified as a demon, and it is possible that he is a Kal'Gerion demon, like the other demonic bosses encountered throughout Daemonheim. Unlike other bosses who are simply 'there' when the player enters the room, Jagex has stated that he has a "dramatic entrance". By looking at the concept art, it seems he may be chained down upon entrance, but it may also hint that the player must chain down the demon to defeat it. One can determine from the Twitter hints image displayed below that he is possibly summoned in some sort of Forgotten mage cult ritual like Delrith from the Demon Slayer quest.

Trivia

 * With the addition of this boss, this is the first time voice acting has appeared in the game aside from the tutorial.
 * On the day of release, Yk'Lagor the Thunderous' music track's unlock info reads "This track unlocks default info."
 * Unlike other bosses you have to help to free him from the bindings of the forgotten mages, before he attacks you.
 * He's one of the few bosses that kills his own minions.