Moss Man is a "nature god" of Eternia and an ally of He-Man. He is a character appearing in the Turtles of Grayskull (mini-comics) and Turtles of Grayskull (comics).
Turtles of Grayskull[]
Upon learning that something had activated the paradimensional alarm, Teela and Roboto rush to Man-At-Arms' workshop to inform him and He-Man. The disruption point is the Swamp of Gangoon and He-Man takes Moss Man and Ram Man with him to investigate. The trio do not return. By The Power of PIZZA!
When the villainous Beast Man shows up at Palace of Eternos, he is quickly captured. He says that Skeletor summoned an emerging power to Eternia, which turned out to be a bridge to another universe. This dropped Krang and Shredder in the middle of the Swamp of Gangoon. Skeletor struck up a partnership with Shredder and Krang to utilize mutagen to conquer first Eternia, then Shredder and Krang's world. Beast Man tells them that he witnessed Ram Man, Moss Man, and even He-Man himself captured and subjugated to the mutagen. Belly of the Beast (Man)
It is revealed during a flashback, as told by Sorceress, that after Ram Man and Moss Man fell to the alien poison (mutagen), He-Man remained on his feet long enough to hurl the Sword of Power as far as he could so that evil could not possess it. The Spirit of Gray-Shell
He-Man, utilizing the Shroud of Shape Shifting, infiltrates Snake Mountain. He uses the Sword of Power to cure his friends, Ram Man, Moss Man, and Roboto. He-Man in a Half-Shell
Moss Man is among the Masters of the Universe, Turtles, and their allies who join the major battle against the forces of evil. Turtles of Grayskull issue 1