Does might go to minus? In that case if I use a combat trick on a unit how does it go?

Yes, Might can go negative.

Here's how it works:

A unit's Might can be reduced below 0. The game tracks the actual value (including negatives) for calculation purposes. But whenever the game checks its Might — such as for combat damage, or for effects that reference "Might" — any negative value is treated as 0 (Rule 143.2.b).

How combat tricks work with a negative unit:

Say you have a 3 Might unit that gets hit with a -4 effect. Its current Might is -1. For combat, it contributes 0 damage, and if it takes even 1 damage it will die (since 0 Might with any nonzero damage = dead).

Now you respond with a combat trick that gives it +2 Might. The calculation uses the unit's current actual value (-1), not the 0 placeholder:

• -1 (current) + 2 = 1 Might

So the unit ends up at 1 Might. It doesn't snap back to a higher value — the buff applies on top of whatever negative value it's sitting at (FAQ #9535). If it was at -3 and you gave it +2, it'd be at -1, still treated as 0 for combat but now only needing +1 more to become positive.