Merethiel is an elf who is involved in the Solak boss fight. She joins players inside of the boss room as both a supportive combatant and a key figure in certain phases of the fight. She is the sister of Erethdor, whom she, her other siblings and Solak fought against when he attempted to take the Lost Grove's power for himself. Though they were victorious, Eredthor's influence was able to corrupt Solak's spirit. He eventually gained complete control over Solak, prompting Merethiel to begin recruiting powerful adventurers in order to free him and destroy her brother once and for all.
^Ruins (The Lost Grove), RuneScape. "Eredthor: The Grove of Guardians!... Sacred they are, but flowing with power. Power for our taking. Think what we could achieve should we harness it... Take it. Bend it and twist it into the unthinkable... Imagine what we could do. We could rival Seren."
^Merethiel, RuneScape. "My brother has fully corrupted Solak's mind, I fear now he's going to succeed in using the power here to break free. You must help me put a stop to this."
^Merethiel, RuneScape. "Losing my brother that day felt worse than if he'd merely died, for I know his soul will linger on, in the stone and Solak, torn and tormented. After he was bound, Solak asked us to deliver the stone to Seren, but as the realization about his eternal gruesome fate set in, the loss was too hard to bear."
^Jagex. Mod Ramen's Twitter account. 7 February 2018. Mod Ramen: "A little mistake I made when doing the Grove, it is actually Merethiel, will get a fix out!"