Heres a little exploit/bug our tanks discovered the other day while attempting Nef HM.
If you spam backpeddle during Ony/Nef's breath it sometimes negates the breath entirely, this made Tank healing in P1 & P3 trivial as our tanks were able to prevent about 50%+ of the shadowflame breaths over the entire duration of the encounter.
They hadn't perfected the exploit but were able to reproduce it several times during the encounter, not really sure what was the specific cause but they found spamming backpeddle anytime during the breath cast would sometimes prevent it entirely, in some cases the breath would play the annimation but cause no damage.
Enjoy Nef HM made easy.