Can units go to negative Might?

Yes, units in Riftbound can have negative Might values.

According to Rule 143.2.b and associated rulings, while a unit's Might can be reduced below 0, it behaves differently for calculations versus interactions:

• For Calculation: The game maintains the actual current Might value, including negative numbers. This is important because if a unit has -3 Might and receives a +2 Might buff, its Might becomes -1, not +2 (as it would if it had snapped to 0).
• For Interactions: Whenever the game checks a unit's Might for game effects (such as during combat, or for determining if it is killed by damage), any negative Might value is treated as 0 (Rule 143.2.b).

Key takeaways regarding negative Might:

• Survival: A unit does not die simply by reaching 0 or negative Might. A unit only dies if it has nonzero damage marked on it that is equal to or greater than its Might (Rule 142.2.a and 143.2.a).
• Combat: Because negative Might is treated as 0 for combat, a unit with negative Might contributes 0 damage in the Combat Damage Step (Rule 143.2.b).
• Lethal Damage: If a unit has 0 (or negative) Might, it is considered to have 0 Might for the purpose of checking for lethal damage. Therefore, it will die if it receives at least 1 damage (the minimum amount of damage).