Fourth wall broken – Starlight predicts the Mane Six are going to sing a song on their friendship retreat. Later in the episode, the attendant in Manehattan Escapes points out how the song caused them to go two seconds over the record.
Flurry Heart episode – “A Flurry of Emotions”, need I say more?
Celestia Glim Glam episode – The second episode (All Bottled Up), natch.
“Just friends” – The StarTrix is strong with this season.