Thunderlane and Supermare growing closer to each other.
Rainbow Dash finally accepts her destiny in the Fortress of Solitude.
And her getting use to her increased speed. "This Is Awesome!!"
Supermare willingly surrendered to a General Ripper just to show her willingness to cooperate.
Thunderlane and Rainbow Dash share their First Kiss.
There's something incredibly sweet about how Soarin' keeps acting respectful towards Diana even when she's going through culture shock.
Cadence is pregnant.
A short story set after the end of Mare of Steel has Rainbow Dash picking up her mother from the hospital Brainiac put her in. Rainbow Dash blames herself for what happened, but Firefly assures her that it's not her fault. It's all rather touching.
Another post-Mare of Steel side story has Supermare destroying a storm with a clap and carrying a ship into port, all so that a father doesn't have to break a promise to his daughter that he'd be home for Hearth's Warming.
Soarin' refuses to abandon Diana even when she asks him to leave for his own protection, because he says he couldn't stand the thought of her being hurt because he wasn't there to help her.
On a smaller note, there's Celestia's absolute faith that Twilight can help Diana and Soarin' fight Ares even without the Elements of Harmony to support her.