Found a guide
Dread Council
NB: The Dread Holocron is a friendly entity that does not block movement or line-of-sight.
The fight begins when any Dread Master is engaged with any ability. Regardless of which Dread Master is attacked, Bestia will always join the fight first. Additional Dread Masters will join the fight at timed intervals.
The Dread Masters' Order of Appearance:
Dread Master Bestia - Bestia is surrounded by an AoE corruption effect; any Dread Masters caught inside this AoE will receive a buff that increases their damage done and reduces damage taken. At regular intervals Bestia will knock-back her primary aggro target; care must be taken so that her target does not get knocked off the fight platform. Bestia will also place a stacking debuff on her primary aggro target; at approximately seven stacks this debuff will one-shot kill any character. Tanks should swap Bestia when her target has five stacks.
Dread Master Calphayus - Calphayus is surrounded by a shield; any damage done to him from outside the shield will be reflected back at the attacker. This shield only affects Calphayus; it is safe to damage other Dread Masters caught within it. At regular intervals, Calphayus will attack a random raid member with Focus Crystals. Calphayus drops red circles below his feet at regular intervals; these circles will cause any players standing in them to receive reduced healing and any Dread Masters standing in them to take reduced damage.
Dread Master Raptus - Raptus uses a frontal-cleave called Deadly Slash (3.5s cast) which will knock-back anyone caught within its AoE. Deadly Slash can be avoided by running through/behind Raptus while he is casting. Raptus will also use Spinning Attack at regular intervals; whoever is targeted by this ability should kite Raptus for its duration.
Dread Master Tyrans - Tyrans will regularly teleport to different locations within Ring 2. He does not otherwise move. Tyrans will regularly cast Thundering Blast on random raid members. This attack does not do much damage normally; however if Tyrans ends up buffed by Bestia or Calphayus this attack can quickly overwhelm the raid group. Since his location is entirely predictable it should be easy to keep him from receiving either buff. Tyrans will also randomly pull raid members to himself. Finally, Tyrans will cast Death Mark on the raid team at regular intervals. Death Mark places a debuff on multiple raid members simultaneously; when these debuff expire the targets will be one-shot killed. There are three different duration Death Mark debuffs each with a unique icon; healers must properly triage the raid team and cleanse the shortest debuffs first to successfully manage this mechanic.
NB: Calphayus's shield is about half the size of its graphic. Players should stand as close to Calphayus as possible when damaging him to avoid reflecting attacks at themselves.
Any time a Dread Master is brought to 50% HP they will jump back to their throne and begin channeling Siphon Energy on the Dread Holocron for 40.0s. The Dread Holocron has a four stack buff; Siphon Energy will remove one stack during the channel, however the stack will return once Siphon Energy is completed. Siphon Energy will also heal the Dread Master for approximately 25% HP at the end of the channel.
Tip: The Dread Masters can be debuffed with abilities that cause Trauma to reduce the healing they receive from Siphon Energy (e.g., Snipers' Shatter Shot, Marauders' Deadly Throw, etc.) This should be done at the end of the channel just before it completes, as this is when the heal takes effect.
The intended mechanic of the first phase of this fight appears to be burning all four Dread Masters to 50% HP at the same time so that they jump back to their thrones and channel Siphon Energy simultaneously, removing all four stacks from the Dread Holocron.
Tip: Due to the need to damage multiple targets simultaneously without tanking them close together, this encounter favors multi-DoT specs (e.g., Lethality Operatives or Snipers).
NB: Everything from this point forward is speculation based on bugged attempts of this fight.
Once all four stacks have been removed from the Dread Holocron the Force ghosts of Dread Master Brontes and Dread Master Styrak (riding his Kell Dragon) will appear.
Styrak places a stacking debuff on his primary aggro target that increases the damage that target takes. Tanks should swap aggro on Styrak at ten stacks (possibly less).
Brontes has multiple frontal cleave attacks and should be tanked facing away from the raid. She may also have a dps rush phase at 20% HP.
NB: During one attempt our group was able to exploit a bug in the fight and kill all of the Masters; afterwards, portals appeared allowing raid members to teleport to Brontes and Styrak's thrones and click on crystals above them. These crystals were non-functional at the time, but are most likely intended to be used in defeating Styrak and Brontes.
After Styrak and Brontes are killed the remaining Dread Masters will re-enter the fight in large forms (similar to the final phase of Styrak from S&V). At some point Calphayus (and possibly the other Dread Masters) will begin channeling Power of the Masters, which may be a soft enrage mechanic.