Thanks for the feedback
It may look impressive, but it is down to breaking down all the components of the battle. Look at the battlefield - the centre is blocked for melee units, so they will very hard time to get to you. So you can leave them for later, and concentrate on ranged units.Shooters - magic dealers and physical dealers. Since dragon has higher magis res., you have to deal with bowmen first. So fear them for 3-4 rounds, repeat if neccessary. You have Concentration 3 = 8 mana/round + occassional pet dragon mana ball, so you can easily afford 2 x fire arrows or even fire rains per round to anihilate the shooters. Use fire arrow to ignite bowmen and bring their numbers down while under fear. Once shooters are down, poison skull cerberi, fire arrow others. Just fly around in the meantime. As you can see from 2nd screen shot it is all doable at level 23 or so while having only cca 60 mana starting pool.