When the Mane 6 get swapped out with Mario on his quest to save Princess Peach, and chaos erupts everywhere. Equestria must now be saved by the hero of the Mushroom Kingdom, and vice versa.
I was hard on myself during my time as Princess Twilight's student. Nothing but my studies had mattered ever since she saved me from my own magic. When I finally burned out, Equestria was on fire.