Trixie VS The Flim Flam brothers. Flim and Flam show up exploiting an absurdly obscure law that allows them to lay claim to Sweet Apple Acres. Trixie, without even throwing so much of a spark of magic, invokes Screw The Rules, My Friends Have Connections to basically browbeat Flim and Flam into giving up and leaving. Flawless victory.
Whenever a battle involves one of the fused forms facing down a Nightmare, it will have at least one moment like this.
FlutterHeavy uses her weapon to pummel Masky Earth Pony with bullets, forcing it to retreat.
AppleDemo blasts away at Nightmare Grave while stickybomb jumping over the rooftops.
EngiRarity keeps Nightmare Doctor on the defensive with some expert use of turrets.
Scoutie Pie, with help of another fusion, zips right past a barrage of laser blast and takes down the powerful Nightmare Harmonic.
RED Medic, using Sasha, stops an avatar of Slenderman from reaching RED Heavy by somehow tapping into the magic that is empowering both their BLU counterparts.
Queen Chrysalis is now a good guy. Heck. Flipping. Yes.
Discord refusing to work with Slendermane. And would "rather become a Bastion of Order" than let him have his way.
Cheerilee getting herself out of Nightmare Gardener through sheer force of will (and help from the Doctor, Rainbow Sniper, etc.)
The Changelings' Big Damn Heroes moment, especially with Chrysalis pretending to be Slendermane.
Trixie transferring BLU and RED Engineers memories of imprisonment (on the distant planet and the Australium mine, respectively) into herself, thus not only relieving them of a collective 3000 years of pain and loneliness, but also having to shoulder them herself! Even better, she nearly goes Nightmare from the pain of it, and fights it off.