Her vocals
The crowd knowing EVERY word, and it not even being a Katy Perry concert.
Her two best songs coming together as one. The fact that you can see a little pixelated Benjamin in the background at one point
Surprisingly a lot of Firework performances there. I assume it's because when she does anything other than terrible at that song it sounds amazing. (Couldn't find a HQ video of Firework @ The big weekend though )
Special Shout out to Dat Guitar in the Prismatic I Kissed a Girl performance though.