In the inky black darkness of the mind realm, the impossble becomes very possble. A blank slate, the plece where heroes reside. However where heroes reside villians reside as well. The mid realm is built from the souls of those that have passed. This realm is closely tied to the others. Those with great mental prowess can harness the raw power of the mind realm to change their world as they see fit. While most use this power for evil there are a seect few wh use this power for the benefit of ponykind. Like Starswirl the Bearded used his magic to create the elements of harmony, generosity, kindness, honesty, laughter, loyalty, and magic. He left these elements in the hooves of the only ones he could trust, Princess Celestia, and Princess Luna, with the element of harmony they ruled for centuries with kindness, honesty, and generosity, and proved worthy of friendship with loyalty, laughter, and magic.
This rule would be opposed by another well versed in the ways of the mind realm, this being was known as Discord. Discord used the mind realm to change the laws of physics causing complete and total chaos. This angered the Princesses, Discord had ruined in one day what took the sisters a century to build. Starswirl advised them to consider the elements as a last resort, but Celestia knew that any other attempt would prove fruitless.The sisters agreed that in order yo put a stop to Discord the only course of action was to use the elements, but he was stronger than they expected. The self proclaimed king of chaos kept Equestria in he palm of his hand for many years before a lone figure helped to weaken Discord, and buy the Princesses enough time to seal him in stone they placed the statue in the garden, to keep watch over him.
In another case of a being of great power abusing the mind realm, is the untold begining of the legend of the Mare in the Moon. Over the course of the years after Discords defeat Princess Luna was contacted by a voice from the mind realm. This spirit referred to himself as Chane, his siblings Hanek, and Teala convinced Luna to listen to their brothers words. Chane's words were extremely persuasive he had convinced Luna that while ponies loved and played during her sisters day, they shunned and slept through her beautiful night. Luna reflected on this and this angered her she became resentful, and on the eve of her five-hundredth birthday she refused to lower the moon out of spite she lashed out and rebelled. Celestia was taken aback she never thought her sister would do anything like this. Satisfied with his accomplishment Chane took his siblings and returned to the mind realm never to be heard from again. Celestia, confused called a meeting with her mentor Starswirl the Bearded. Starswirl advised that Luna could not have coe to ths conclusion on her own. He thought that maybe her magical prowess made her a target for a bigger threat than Discord. He went on to explain that he knew a unicorn with the power over fear, and his brother held power over hate.
Starswirl continued that these unicorns were just as powerful if not more than himself. Celestia was suprised by these words she had never thought anything was more powerful than her master. If these unicorns were even possibly more powerful than her master Celestia thought that they could have easily convinced Luna and maybe even herself. Starswirl had come to a conclusion Celestia must do to Luna what they had done to Discord. Celestia cringed at the thought of turning her sister to stone. Celestia went to think about what she had to do. After intense research Starswirl had found a way around turning Luna to stone. If she was banished to the moon she may come to her senses, and be returned to her previous form and disposition. But in order to send Luna to the moon she must willingly relinquish her connection to the elements of harmony. Dark times fell upon Equestria Celestia knew what she must do she must banish her sister to her namesake.
The lone figure had appeared once more to help the Princess combat this darkness. After hours of heated battle Luna became exhausted, the figure saw this chance to use the mind realm to contact the real Luna. The figure explained what she must do. Luna accepted this drastic measure on one condition that the figure finds new holders for the elements. The figure agreed to this condition and returned to the realm of the living with the news of Lunas choice. Celestia used the elements of harmony one last time to send Luna to the moon. And you know the rest.