A new mirror like the Crystal Mirror had appeared in Twilight Sparkle’s castle, seemingly composed of machinery and pipes filled with red and blue fluid. Out of this mirror came a colt that looked exactly like Twilight!
 
This gender-bent doppelganger, calling himself Dusk Shine, claimed to have come from a world where Equestria was divided into three warring regions by a gigantic wall that sprouted up ever since a mysterious cube was discovered. Together with the male version of Ember, Dusk Shine defended the people of his Equestria from the chaos of the war, until he was thrown into Twilight’s world by an evil entity that fed on conflict and who had created the wall.
 
Now Dusk Shine seeks a way to return home before it is destroyed by war, as well as using his powers and scientific knowledge as Masked Stallion Catalyst to protect the inhabitants of the world he has been thrust into.