Maximising Halfus HC Demonology DPS

[morpheeus]

Hi all,
This is a question to all locks really,im having trouble sustaining high damage on this fight,At first i AOE everything whilst the adds are up but im a little unsure whats the best thing to do after that?

Any help would be greatly appreciated

Morpheeus (Phil)

[Jubeto]

Multidot and Hellfire