20Rangers of Two Worlds
“Rangers of Two Worlds” marked the first official crossover between seasons of Power Rangers. The Alien Rangers of Aquitar, who had temporarily appeared for their own short season when the Mighty Morphin Power Rangers were de-aged to children, returned to team
up with the Zeo Power Rangers.
This episode marks the last appearance of one of the original Power Rangers, Billy, as star David Yost left the series prior to filming. Billy had begun rapidly aging thanks to the technology that had previously allowed him to age while the rest of the Rangers were still children. While the Rangers tried to find a solution, Lord Zedd and King Mondo were intent on destroying them, unleashing multiple monsters on Earth.
The Alien Rangers returned to Earth to not only help with Billy’s aging problem, but also to defeat the monsters. In the end, Billy went to Aquitar, where he was returned to his normal age, and decided to stay. It’s one of the most straightforward crossovers the series ever did, though as the years went on, they certainly got crazier.