Hmm... Does the Rainbow Dragon attack for 5 squares when it's lucky? That's not luck, it's a trap: imagine your own troops are standing behind the enemy, and suddenly 10 dragons breathe on them!... the outcome is sad...

I often had a similar problem - the units on the battlefield were positioned in such a way that the dragons had to "wait" or lose a turn just to change position, only to avoid burning half a stack of your own "native" fairies or dancers with a 2-square breath attack standing behind the enemy...