As everyone will know, Discord in an alternate equestria is a superhero who fights against the tyranny of Celestia, and with recent comics we see that Discord at least in the IDW universe has a cousin called Eris. Giving a funny coincidence with Superman, he has a cousin and an alternate version of himself, so I found it curious how Eris of Equestria 3 would be.
Inhabitant of an utopia called Wonderland, a place inhabited in a pocket dimension, where there are draconequus, a latent race to have material handling skills if there was a trace of chaos around it, trying to keep it non-existent to avoid a civil war.
She is a niece of Dis-rray, the greatest scientist of that dimension who discovered an inevitable end of the dimension due to instability in the dimension, which caused a family conflict, since Er-is's parents believe they could save Wonderland if they caused chaos to awaken their latent abilities, trying to manipulate the stability of the dimension, meanwhile Discord's parents believed it was useless and would make matters worse.
Despite the disagreements of the families, Discord's mother, Dis-nomia, had a good relationship with Er-is for being the most sane of her family to such an extent that Dis-nomia convinced her husband to accompany her a baby Dis-cord in the inter-dimensional portal that has very little energy for a trip with just 2 people if he did not want catastrophic events to happen.
While assimilating and preparing to go with Dis-Cord to the portal, the laboratory was invaded by his parents who awakened their abilities and searched for Er-is to demonstrate that they are capable of saving the world.
Dis-cord's parents wanted to send the 2 children outside Wonderland while Er-is's parents try to avoid it because they consider it unnecessary, they just need to trust, trying everything and failing in the attempt, causing anger as they consider that Dis-Cord's parents are very few patients, trying to kill them to prevent escape while Wonderland was collapsing.
During the interdimensional trip, both children were separated in different places because of the failures that the portal had thanks to the intervention of Er-is's parents, she arrived at the Crystal Empire to be cryogenized on the road meanwhile Dis-cord I arrive in Ponyville to be received by some apple farmers.
She discovered that she had the same abilities as her cousin however, she was unstable with her abilities due to a genetic condition, so she had to limit herself to affecting the luck at will not to die.
At first her cousin was her mentor and roommate to avoid being harmed in case they discover their relationship, having a somewhat complicated relationship because of their difference in powers and lost years, seeing their cousin differently.
At the beginning of his career as a super hero, he had good chemistry with his cousin under his mask so as to instill a great confidence in the audience hungry for hope but then he became bitter since he could not remove the image as his cousin's assistant, generating an inferiority complex.
So he decided to move from town to have a new identity as Greatest Girl, so as not to be consumed by his inferiority complex and thus be tempted by evil.