Franz seems to have made up a damage value when pressured.

Repro-steps :

1. Go to the deepest part of the Silver Vein Mine, accompanied by Manah.

2. Spot the boss at the end before it sees you.

3. Coordinate a surprise attack on the boss.

4. First Notice that Franz doesn’t make anyone roll to hit, and just gives you the hits for free.

5. Roll for initiative when prompted.

6. Notice, when the encounter starts, that Franz correctly detected the surprise attack but failed to account for the boss starting the encounter in a damage state.

7. Call out Franz for not damaging the boss.

8. Notice that in reaction he reduces the boss’ health by 25 when both damage dice are 1d6, meaning without a critical hit (which you didn’t roll for) the maximum damage is 12.