Can Frozen Fortress and Thousand-Tailed Watcher be combined to kill enemy units by dealing 1 damage in the Beginning Phase and then reducing their Might later in the same turn?

Ruling: Yes. If Frozen Fortress deals 1 damage to enemy units during the Beginning Phase, and you later play Thousand-Tailed Watcher during the Main Phase of the same turn, the Watcher's -3 Might debuff can reduce those damaged units to 1 Might. When a unit has damage marked on it equal to or exceeding its current Might, it is killed during the next cleanup check.

Sequence:

• Beginning Phase: Frozen Fortress triggers and deals 1 damage to each unit at the battlefield
• Main Phase: Play Thousand-Tailed Watcher, its ability triggers and resolves
• The Watcher's ability reduces enemy units' Might by 3 (to a minimum of 1)
• Cleanup check occurs: units with 1 Might and 1 damage marked are killed

Nuances:

• The Watcher's "this turn" effect includes both the Beginning Phase (when damage was dealt) and the Main Phase (when the debuff is applied)
• Units are only killed if their Might is reduced to equal or less than the damage already marked on them
• This combo works on units with 4 or less base Might, as the Watcher reduces Might to a minimum of 1