While resolving Zodiark's second ability, you choose half the non-God creatures you control (rounded down), then each other player in turn order does the same
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
Also, for this set, when they refer to Booster Fun, they mean one of the following treatments: Artist Rare, Woodblock Rare, Borderless Character, Borderless Lands, and EA Legendary Cards
Vigilance I Exile target artifact, enchantment, or tapped creature an opponent controls
Some of the cards and scenes mentioned in the lyrics of You Can Fly! seem to hint at those theories, with recent reprints maybe lending them a little more weight
If you like the look of the Boulder but want space to put tokens and dice, there is also the Ultimate Guard Boulder N Tray