[Spoilers C4E17] Theory on Tachonis and Tannesar as well Occtis return

Tansuls ritual vs Tacchonis Ritual

Tannesar was created by Tansul in the event of his death to create a celestial. A Celestial whose mission would be avenge and maybe resurrect Tansul. This Celestial  was fittingly called Veda Vindictus  which can be translated as Angel of Vengeance

To create the Celestial, someone of Tansul’s priestly bloodline(Tachonis or Halovar) would be sacrificed,and their heart would be brought to Tannesar.The heart would be presented to the Apotheosis Obelisk in Tannesar and The ritual would begin. The Ritual would summon the soul of the sacrificed person and resurrect them in a Celestial body with their mind brainwashed to do Tansul’s last wishes. 

The Tachonis want to use Tannesar to create a Celestial but not not one Tansul intended. They dont want to create an Avenging angel of Tansul.They want to create a Psychopomp Angel loyal to the Tachonis.Probably because a Psychopomp angel(Like Olbalad and the Nightingale were) would grant them access to the realm of the gods and allow them win the war in the Underworld.

So to fufill their goals, The Tachonis had to modify the Tannesar ritual by adding something called Calcidion prothesis. Below is how i believe the modified ritual works

1.Obtain the bones of a Celestial Psychopomp(Called Calcidium )

2.Choose a Tachonis or Halovar to be the Sacrifice.

3. Place the bone piece in the body of the chosen Sacrifice to cause bonding. This procedure is called Calcidion prothesis.This procedure ensures the Celestial created will be a Psychopomp

4.Take the Heart of the Sacrifice to Tannesar to the Apotheois Obelisk triggering the Ritual of Tannesar,

5. Ritual creates summons the soul of the person who was chosen to be the sacrifice to Tannesar. That soul is reborn as a Celestial .And because of the Calcidion Prothesis the  Celestial will wield the power of a Psychopomp  but it will be one loyal to the Tachonis not Tansul.

However executing the Ritual is not easy. As we saw from the letters in episode 17, Tachonis have had many failed experiments to execute this because they kept failing at Step 3 the Calidial Prothesis.

The Calicidion Prothesis failed when a Halovar sacrifice was chosen because Halovars are immune to the procedure

The Calcidion Prothesis  also failed when a Tachonis was chosen because of the Tachonis innate gifts and connection to Tenebral Reaches, 

So the Sacrifice had to be a Tachonis who was not a Shadow sorcerer. Thats why Occtis was perfect

Why did Occtis Ritual Fail

Step 1 to Step 4 was executed perfectly for Occtis. The Calcidion used for the ritual was the Stone of Nightsong, and Calcidion Prothesis worked fine on Occtis. Primus took Occtis heart to Tannesar and triggered the ritual. That was he was able to begin to pull Occtis soul to his location, Tannesar.

Occtis soul carried a portion of the Stones power because of the Calidion prothesis. However whilst Occtis soul was travelling, Occtis woke up(Thanks to Thaisha) fought back and ripped out of his soul the Portion of the Stones power within it.He doing so unraveled him leaving him stuck between life and death, The Portion of the Stones power Occtis ripped out of himself became a Flock of Nightingales and that is what Primus ended up summoning in Tannesar.

Occtis soul was unraveled and stranded in Limbo but it was still anchored by the Calidion prothesis to the Stone of Night Stone.When Bolaire and Murray did their magical surgery on Occtis, they did something incredible.They not only pulled the stone from Occtis body, they did it in a way that tugged on the connection between Occtis stranded soul and stone essentially pulling Occtis soul or what remeained of it from Limbo back to the land of the living.Occtis lives because hes anchored in the Land of the Living the Stone of Night Song. v

What Happened in Tannesar

The Tachonis were attacked by a mysterious robed group during theritual in Tannesar. However the Tacchonis was expecting them which is the real reason they recruited the Barrowguard. A fight ensues.

To make things worse, the Ritual fails. Occtis soul isnt summoned, instead the Flock of nightingales is summoned. The Ritual instead did something horrible. Something was unleashed in Tannesar, that forced Primus to abandon it. Something was unleashed that forced the surviving members of Tannesar to hide deep in it and they are trapped there. Alogar is one of them