Does Janna's healing ability remove the -3M debuff from Watcher, or does healing only work against marked damage?

Ruling: Healing clears marked damage from units. Healing does not negate effects like Watcher's that lower might.

Nuances:

• If you want Janna to heal units after they take damage from an action spell, you need to play Janna on a new chain after the damage spell resolves
• If Janna is played in response to an action spell like Wages of Pain, Janna's ability resolves first before the spell deals damage