Zarrakon is a tricky encounter which can involve a lot of luck until you have it on farm.
You need four tank groups with a decent amount of DPS in each.
Groups should generally consist of 2 healers, a tank, bard, chanter and a DPS - including the MT group.
The nastiest AE he has is the nox which needs to be instantly cured due to the power drain attached. The heat based AE is a bit random but generally doesn't hurt too much.
Strategy Overview:
Fail Effects - Purple/Red Screen: Two visions which must be cured quickly by running to the corresponding pool situated either side of Zarrakon.
Add Curse - Throughout the fight one group out of the four is cursed. The curse allows that group to attack/kill an add that pops peridocially. Only that group can attack the add and anyone outside the group cannot cast beneficial spells on the add group (apart from Rezzes). Bear in mind the MT group can also get the curse in which case a tank switch is required.
General Strategy - Raid stands either in front or side on to Zarrakon due to a huge Tail Swipe. Joust the nox to between 10 and 15 metres (optimum distance for power drain/HP Damage) Lots of DPS on Zarrakon, lots of power management, efficient tank switches if the MT gets the add/visions. Loot chest.