The most obvious strength this deck has is its ability to Frighten.
With Princess Luna, Night Mare x2
Thunderclap (Event) x3
Pony of Shadows (troublemaker) x1
and with Rainbow Dash, Goosebump Giver x3
added to the mix the simple action of exhausting her will Frighten yet another opponent's Friend, costing your opponent 2 Action Tokens to Rally each frightening Character!
~ ~ ~Faceoffs
However the Princess Luna deck isn't a one trick pony!
Build up a small arsenal of Events (including the above listed 3) to back up Starry Eyes, Space Cadet x2
will allow him to power up for faceoffs.
Also use Events to power up Princess Luna (boosted) for her +3/Event bonus as well!
Eclair Creme, Vicarious Listener x3 can help during the Scoring Phase and with Problem Faceoffs
Canterlot Archives can swing your draw card for faceoffs to help win
and with What Went Wrong? you can negate your opponent's high card from their faceoff draw card.
~ ~ ~
Use the synergy between Twilight Sparkle, All-Team Organizer x2
to generate an extra Action Token, and Rainbow Dash, Weather Leader x 2
to ready Twilight Sparkle to generate yet another Action Token!
~ ~ ~
Movement: Faster Than Swift!
And finally (in addition to Friends with the Swift ability), playing Friends like Rumble, Fast Learner
with Rainbowshine, Cloud Wrangler
can have a cascade effect for exhausting a Friend to move them, and then immediately ready them!