Does a unit with 0 or less Might automatically die?

No, units can stick around on the board with 0 (or less!) Might. They will die if they take any damage, but “0” is not a valid amount of damage, so it takes 1 damage to kill a unit with 0 or less Might. We realize that this is a little weird, but it’s important to us that cards like Frigid Touch can’t be used to actually kill units, only weaken them.