As I lost in the swiss to his Red/Green aggro I was a bit afraid of not making it to the finals, but I got a bit lucky with an early Abyss in the game and Millstone ending it fast.
We then came up with the idea of a card that listed all the possible double-faced cards in the set, which we called a checklist card
Im Andy, and today were taking to the skies with damage so nice were dealing it twice
Take Half-Squirrel, Half- as a great example
In short, it keeps cards safe and makes sure all information is on the table between parties interested in selling rare cards
You can produce a Map token with it that's used for other finalities in the deck, or simply explore into your 1/1 flying creature, which can produce a 2/2 flier or give you a land