Protip: A good strategy is to use your character with the highest HP as tanks and guard with characters right behind them shooting projectiles, and mages right behind them as well, healing the tank every turn. the AI is not very smart and will always just go for whoever is closest to them, so you can basically tell them who to attack if you position your troops just right. Remember to recruit everyone you can, since your own HP doesn't increase as you go through the levels, but the enemy HP does!