The Opening TP, set in 1997, involved the "early" arrival of Unicron. Optimus Prime tried opening the Matrix to use it against Unicron, but failed. Instead, the Autobots and Decepticons teamed up with an alien ally to defeat Unicron through more conventional means.
Meanwhile, Dr. Mindbender discovered a way to reverse the aging process of humans, and experimented with captured G.I. Joes. The plan backfired, however, when the Joes escaped, taking a large sample of the de-aging formula with them.