Magic has faded, but the war rages on, powered by diesel. Most think Captain Rainbow Dash is an old burned out warpony, waiting to die on the battlefield. Maybe they're right. Maybe even Rainbow Dash doesn't know.
Sweetie Belle struggles to get closer to her sister in the midst of a tragedy that hits too close to home. Meanwhile, Rarity struggles to make a better life for her sister and herself in the midst of said crisis.
Sweetie Derelle, the alternate reality Sweetie Belle, has arrived in Equestria to save everyone. That includes driving a bus at high speed through Canterlot to make sure it doesn't explode. Also into Canterlot Castle. Specifically Celestia's Bedroom.
On Hearth's Warming Eve, Sweetie Belle comes across a lonely Sugar Belle and invites her caroling, where the two Belles confide in one another about life and cutie marks.
Sweetie Belle wonders what is running through Opal's mind when she attacks Rarity one morning. During Twilight Time she runs across a spell that allows animals to talk. She memorizes it and casts it on some of the pets.
Sickness does not need to mean isolation. As two ponies come to her in a time of need, Sweetie Belle comes to understand that. Some lighthearted d'aww of Sweetie and a hospital visit.