I like your idea of Breath of the dragon which would vastly add to the whole slow and poison them nature method.
Disclaimer
A few N2's casting poison ward would put a wet blanket on this. However it is only 50%. They could be facing 2 or more poisonings from range spells. Then snake bladders and the mossbody if they hit you. Haven't tried it but it sure sounds nasty.
Don't forget your Pretender can also Doom which might afflict any that escape death from poison. He can also Will of fates for Luck on all your troops.