The Charizard GX Secret Rare holds the edge in rarity but isn't the most valuable Charizard in the set
Sure, you might not make a ton of money selling two Revised Volcanic Islands, maybe $50, but they are high-demand cards that are easy to move, require no sorting, and likely ship together, so all in all, you're making that $50 for very little work
There are two cards featuring her: Yuna, Hope of Spira which can be found in the Main set, and Yuna, Grand Summoner which can be found in the Commander Deck
Addendum If you cast this spell during your main phase, put a +1/+1 counter on each of those creatures and they gain vigilance until end of turn
I see the "flip planeswalkers" as an inflection point were designers became empowered by the idea of these two-step stories
To be honest I was surprised this card wasn't ranked higher