Essyllt is a member of the Iorwerth Clan and the true head mourner of West Ardougne. During the Regicide quest, after the player exits the Underground Pass with the help of Morvran, he slays Idris to deceive the player into helping the Iorwerth plans instead of those of King Tyras.
He appears in Song of the Elves at the side of Lord Iorwerth, killing Ysgawyn during the attack on Lletya. He later confronts the player when they and the elven clan leaders attempt to seal the Underground Pass, critically harming Elena in the process. Players must dispatch him to continue the quest.
During the boss fight, he mainly attacks with melee. Occasionally, he will stun the player and quickly shoot an arrow that deals up to 43+ damage. This attack can be blocked with prayer if the player is fast enough. He also occasionally shoots a blue orb that drains all the player's combat stats by 5.
After completion of Song of the Elves quest, Essyllt can be fought in the Nightmare Zone minigame. However, the hard version of Essyllt currently has double the stats of Arianwyn in normal mode rather than double his own stats in normal mode.