You lose the option on playing it for black and you have to exile the things you return but you will be sacrificing your stuff before then so it doesn't matter a jot
If neither stat of the new creature is greater, the ability will do nothing
Although there is no guarantee on which cards will be pulled, the statistics from previous sets suggest each box should include 3 to 6 Legendary and 1 to 2 Epic cards
Celes was considered for 6 since the deck is focused around the World of Ruin and the second half of that game, while Yuna was considered for 10 as a fan-favorite
once both are on the field with a single Squirrel, you can sacrifice the Squirrel to Chatterfang, create a Treasure from the Plunderer, and Chatterfang will see that Treasure and create a new Squirrel
It's advice that Brown echoes, saying that local game stores should "consider reserving some Play Boosters to use for play throughout the season if [they] anticipate running out ahead of time."