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
If neither stat of the new creature is greater, the ability will do nothing
As for Commander, he's been playing since 2010, when he started off by making a two-player oriented G/R Land Destruction deck
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."