ThunderCats - Season 1 Episode 20 Return to Thundera

The Thundercats briefly show Lion-O how the time capsule they recovered from the caveman works. Curious to see more, Lion-O activates it during his night-time watch, and gets caught in its projection rays. The rays send him back in time to Thundera, just before the final tremor that destroyed the planet. Meanwhile, the Mutants have built an evil robot monster that is destroying Cats' Lair. Back on Thundera, Lion-O encounters his father, Claudus, and saves him from a Mutant attack. In return, Claudus gives Lion-O the plans to the robot that was attacking the Thundercats in his own time.