As for the songs, Be Our Guest and Look at This Family help you find any needed characters, and with two copies of Ariel - Singing Mermaid, we don't need to invest as many characters to sing
The beauty of this combo is that all those Cursed Mirror copies have haste so they can immediately attack the table with a swarm of combat damage
The flying ability helps as well here, giving Avacyn some much-needed evasion to do so
Now, this philosophy only applies to the cards that are the most sought after, which isnt always the rarest version of a card
Even if the curser doesnt then wipe all the now measly minions from the cursees board, it becomes so much easier for anyone else at the table to destroy them, not to mention just attacking
Rose Tyler's card, meanwhile, references the moment she stares into the Heart of the Tardis and becomes Bad Wolf