There is a bigger fireball spell (placed in slot 2 if I remember well) that can destroy big areas.
There are areas with a nest (or an electric tower) in the middle and several towers around, target the central one and use this spell to destroy the whole area.
Use the spell in slot 1 (the small fireball) to lower the life of the target while you approach then dive and finish with the fire breath.
From the middle part you get an additional "spell", you can request the zeppelin to strike a target (slot 7).
Good luck.
Imarion
