If a 5 might unit battles another 5 might unit, and one receives -1 might from Stupify, do they still trade?

Ruling: No, they do not trade. The unit with Stupify applied (now 4 might) dies, while the 5 might unit survives.

Nuances:

• Damage marked on a unit does NOT decrease its might (a 5 might unit with 3 damage marked still deals 5 damage)
• Effects like Stupify DO decrease a unit's might
• A unit with damage marked on it still deals its full might in combat, but requires less additional damage to be destroyed