Masks does not advance on XP from kills. It advances on Potential.

A young hero marks Potential every time they roll a 6 or under, every time they reset all their labels, every time they Pierce the Mask of an authority figure, and every time the GM hits them with a custom playbook trigger.

When all the Potential boxes on the playbook are marked, the player clears them and chooses an Advance from the playbook list:

• Take an advanced move from your playbook.
• Take a move from another playbook.
• Add +1 to a label (max +3).
• Unlock your playbook's adult moves.
• Take an entirely new playbook (rare; reserved for narrative shifts like the Janus going public).
• Lock a label.
• Take an Advanced playbook (Halcyon City Herald Collection).

Locking a label is a final-act decision. A locked label cannot be shifted by anyone. It is the hero saying, in mechanics, "this is who I am — and you do not get to argue." Locking ends the playbook's identity-tension engine, which is why it usually marks the end of the playbook.

Endgame: when a hero has locked all five labels or unlocked all the moves on their playbook, they hit the Moment of Truth — a single scene where the GM hands them their adult self, full-power, no constraints, for one act. After the Moment of Truth, the hero either retires the playbook (and starts a new one) or transitions into an adult playbook, if the campaign is using Halcyon City Herald Collection.