Consequences

Create 5-10 consequences that a PC might incur when they use the arcanum's mysteries. If you write 6 or fewer, give some of them multiple checkboxes to indicate that they can be suffered multiple times. A major arcanum should have ~8 checkboxes total.

Make 2-3 of the consequences not-so-bad, maybe even beneficial. But by the time the player is marking the fourth or fifth one, things should be feeling grim.

Consequences might involve…

… suffering harm/debilities/conditions;
… physical mutations/changes;
… changes to the PC's perceptions, thought processes, and/or instinct;
… benefits like +1 Armor, increased HP, resistance to certain harms, etc.;
… changes to how others perceive the PC
… introducing a new threat or danger
… unwanted attention;
… new, problematic custom moves;
… a task the PC must perform;
… chaos wrought upon the larger world;
… the loss of the arcanum or its powers;
… some combination of the above; or…
… anything else that makes sense.

It can help to think of a major arcanum as a threat, with the consequences acting as grim portents and impending dooms that the player gets (has) to pick.