The origin of moss giants isn't explicitly explained in the game. I have 2 hypotheses
One speculation could be that moss giants are creatures that evolved or mutated in environments rich in moss and vegetation, hence their name and appearance. They might have adapted to thrive in these environments, becoming formidable adversaries to players who venture into their territory.
Another possibility is that moss giants have a magical or mystical origin, perhaps created by ancient wizards or beings as guardians or protectors of certain areas. This could tie into the broader lore of Gielinor, the world of RuneScape, where various magical creatures and entities exist.
