I found that really the only challenge for my party at this fight (and the one before) was keeping Astarte alive. Astarte's AI seems to go crazy every once in a while in gets too close but most of the time she stayed far enough from the big elemental attacks.
My own characters barely took any damage except from a few of the summoned death knight types.
The summons are easy to deal with via status effects and barely do any damage. Just HP sponges The Dragon itself goes down slow but easily. The first stage was harder but neither were particularly challenging. Mainly because occasionally a Death Knight would get close to Astarte. Both fights are long due to the HP bloat.
SoulSap is incredibly helpful on the dragon. Anything that helps hit chance to make the fight go faster.
