Etheria’s secrets unlocked: It was also revealed in season four that Mara, the first She-Ra, had moved the planet of Etheria to a pocket dimension so that the planet couldn’t be used as a mass weapon, as originally intended by First Ones, and what is known as the Heart of Etheria Project. Glimmer, seeing no other way, unlocks the project to give herself and the other princesses unchecked power so they could defeat the Horde, but she also brings Etheria out of the parallel dimension into the real universe, leaving them vulnerable to Horde Prime. This also brings Etheria into the Masters of Universe timeline, leaving season five open to bring in some other original characters from that universe.
Netflix