During The Corsair Curse, the player uncovers that the curse that has befallen the crew was actually Ithoi poisoning the crew's dinner, due to Captain Tock's consideration of firing him and replacing his position as second-in-command with Francois, Arsen's brother, as they no longer need a navigator now that they have settled in the Corsair Cove. By "cursing" the crew with poisoned food, Ithoi hoped that he would be able to stay with the crew due to his knowledge of curses. He too pretended to fall under the "curse". The player eventually proves that Ithoi was responsible for poisoning the crew and faking the "curse", so Captain Tock has the player kill him for his treachery.
He is a capable mage, being able to use elemental bolt spells as well as the Curse spell.
- Using any variation of abyssal whip on him while he is lying down will cause him to say Arrr, RuneScape isn't that sort of fantasy game, in case ye hadn't been told that a-fore today.
- This is a reference to Mod Ash adding additional dialogue when attempting to use one on an NPC who is tied up during the Carnillean Rising quest in RuneScape 3. The Corsair Curse and Carnillean Rising quests were both developed by Mod Ash.
- In Nightmare Zone, Ithoi is renamed as the "Corsair Traitor".