Each player participating in the battle must choose one card from their hand and hold it face down in front of them (unless they have no cards left in their hand; in that case they don’t have to put a card in). Then they all reveal their chosen card simultaneously.
If you reveal a Battle card, its +STR bonus will be added to the total STR of your figures in the battle. Also, any special abilities listed on the card takes effect at this point. If, however, you reveal an Upgrade or Quest card, it adds nothing to your Strength in battle and has no effect.
Each clan adds together the STR of each of its involved figures, and adds the +STR bonus offered by their played Battle card (if any). This is their clan’s total STR in that battle.
Note: If a card’s special effect causes a player to lose all the figures he had in the battle before comparing STR, that does not mean that clan is out of the battle. The figures were destroyed in the course of battle, and the clan might still emerge victorious if its played Battle card has STR enough.