Arrg is a quest monster that must be defeated during Troll Romancequest. All mountain trolls are named after the first thing they ate or tried to eat. Arrg, however, makes an exception. With some trolls, the name of what they first ate is unknown. This is the case with Arrg, so he was named after the sound made by the first thing he ate. This is the same case with Ug and Aga.
Arrg is one of the strongest Mountain Trolls in RuneScape, and uses melee and ranged, both of which can hit up to 649, although the Fremennik round shield reduces the maximum damage from ranging to 200. When fighting him, it is recommended to wear at least rune and have a high combat level. He teleports the player to the Troll arena to fight, and the player is teleported back to Troll Stronghold when he is defeated.
It is best to use a combination of protect from melee and ranged prayers against him and switch prayers as he switches attacks. His attack speed is equivalent to that of a whip, and also have fairly high defence, so this can be tricky. Arrg can only be fought during the quest, and afterwards in the Dominion Tower. If you talk to him after the quest, he will say, "Oh mighty man-warrior, please no hurt Arrg."
Arrg used to have a combat level of 113, the same as that of the Troll generals (before their combat levels were increased in February 2012). His max hit and life points are also the same as those of the troll generals.