Mysteries

Write out the back of the minor arcanum, the custom move(s) and/or follower(s) gained by a PC who unlocks its mysteries. If the arcanum has different tags once it's unlocked, write them here.

Try to reflect the origin, theme(s), and characteristics that you identified when conceptualizing the arcanum. Does it house a spirit or sentience, or call one up? Create that entity as a follower. Does it allow a PC to learn a spell/ ritual, or does it produce a magical effect? Think about how that magic might work, and write a custom move or two reflecting the arcanum's theme(s), function, drawback, and usage (Book II).

See Writing moves for advice on writing custom player moves. Use existing minor arcana and playbook moves for inspiration and guidance. And remember: not every move needs to involve a roll!

Edit aggressively, boiling your text down to the bare essentials while maintaining clarity. You can fit only ~150 words on the back of a minor arcanum card.

Don't be afraid to modify an arcanum after you see it in play. If it's unclear, disruptive, or otherwise unfun, talk to the players and change it. An arcanum isn't actually a set of runes carved in stone—it's just a little piece of paper and you're allowed to make revisions.