Rule 142.4.b

Lethal Damage for a Unit is a non-zero amount greater than or equal to that Unit’s Might. Example: A unit has 5 [M] and 3 damage marked on it. Frigid Touch is played targeting that unit. When it resolves, the unit’s Might becomes 3, and it will have lethal damage marked on it. Example: A unit has 0 [M]. In order to have lethal damage marked on it, it must have at least 1 damage marked on it.