Hi, does this units action trigger multiple times when multiple units in that zone get 1 damage simultaniously? For example when I attack with six units including Friedrich Hemmler and Celestial apprentice. All 6 units get 1 damage, but not sure due to timing window if the action triggers only 1 time or 6 times.

Primus_Magicus said:

Yes, it triggers each time a unit in that zone receives damage. You must put those triggered action on the chain at the next available opportunity (first action window after attackers are declared in your example), and then resolve them 1 at a time.

Action: When a unit in this zone is dealt exactly 1 damage, deal 1 damage to target unit in any corresponding zone.