Nightmares are a unique resource that cannot be collected mid-run — they are granted at the end of each attempt, including failed ones. The amount awarded scales with how far into a run you reached before dying and is amplified by equipping certain Nightmare-category Arcana Cards. Players still learning the game naturally accumulate Nightmares at a healthy rate as their skill improves.

• Unlocking and upgrading Nightmare-attribute Arcana Cards on the board
• Meeting possession thresholds required by certain Cauldron Incantation recipes
• Providing a parallel upgrade track to Shadow (Darkness Crystal), ensuring Arcana progress is not bottlenecked by a single currency

Nightmares function as a "consolation currency" — the more you die, the more you earn, creating a natural catch-up mechanic. Because they are entirely separate from in-run drops, there is no opportunity cost to dying partway through a run. Players who repeatedly hit a difficulty wall will find their Nightmare stockpile growing steadily, giving them the resources to strengthen their board before the next attempt.