Finn Mertens (Farmworld Finn) is the character that Finn would be after he wished for The Lich to have never been born, in Prismo's Time Room. This all occured in the episode "Finn The Human," but he is seen again in the episode "Jake The Dog." He is the son of Mr. Mertens, and owner of Farmworld Jake and Bartram, who he calls 'Bar-Bar' as nickname.
Mertens has Finns clothes but both his shirt and shorts are long and his right arm is robotic like. He has no shoes and has a long nose and big eyes.