When Guardians of Koilos enters the battlefield, you may return another target historic permanent you control to its owner's hand. (Artifacts, legendaries, and Sagas are historic.)
A card, spell, or permanent is historic if it has the legendary supertype, the artifact card type, or the Saga subtype. Having two of those qualities doesn’t make an object more historic than another or provide an additional bonus—an object either is historic or it isn’t.