Recommended: Firebreath, Fire Sphere, Dragon Burst, Summon Friend, Dragon Spirit.
A basic ability, breathing fire is always useful.
Another basic ability, a fireball. It doesn't work of towers.
Transforms another dragon into a ladybird, a definitely useless ability.
A huge fireball which spreads around - useful against a large group of enemies, doesn't work on towers.
A second dragon which turns the enemy attention but dies quite easily. However the cooldown is short.
A shield which takes away stamina.
A very useful healing skill. It's less useful than potions, but there's not always time to change into human form.