Justice League of America, Vol. 1 #91 (1971)

Earth--The Monster Maker / The Day the World Melted / The Hour Hourman Died
An alien and his pet have a psychic link, but a space anomaly sent them to two different Earths. The JLA and the JSA must team up once more to deal with the resulting crisis. Three aliens are out on a joyride alongside their symbiotic pets when they lose control of their ship, resulting in the alien A-Rym being separated from his pet as they travel through the dimensional barrier separating Earths 1 and 2. As the JSA face off against A-Rym, he defeats them, as a result of the adult Robin charging in headstrong. Meanwhile, on Earth-1, as Batman leaves the JLA for another case he's working on, young college-aged Robin faces off alongside the team vs. Teppy, A-Rym's symbiotic pet, with the same actions and consequences. To be continued...
Release Date: 1971