Invest in "[skill] Shield" and "[castle] Altar". The altar will increase your mana total + mana regeneration and the shield skill will grant your warriors invincibility for 20sec (when maxed out). Once you start a battle, all you got to do is save up 200mana and charge. You'll be able to use shield twice and by the time the second shield is gone, you'll have regenerated enough to use a 3rd time. Giving your warriors a full 60seconds of invincibility. The spell take approximately 2 seconds to cast so if you time it right, you won't be vulnerable at any point.
 "Epic War 4"){kind=icon}
 "Champions of chaos"){kind=icon}
 "Agony: The Portal"){kind=icon}
 "Swords and Sandals Crusader"){kind=icon}
 "Arcalona"){kind=icon}