Rogegrain the Sly occasionally turns a player who hasn't Taunted him into a goat. The player must go around and consume the Sweetrolls that spawn to turn back into their original form.
Throughout the fight the boss summons numerous adds including Death Hoppers, Watchers and destructible Portals that spawn adds. Rogegrain also spawns large AOEs that spew out smaller AOEs and will afflict a player with a debuff that can be cleansed with the friendly AOEs that spawn.
Rogerain also has a heavy attack that targets whoever has the aggro which must be Roll Dodged or Blocked.
Eliam Merick is a bit more complicated than the first boss. This boss applies a similar DoT debuff to whoever has the aggro, the tank ideally, like the Veteran Blackrose Prison bosses do. The boss tends to pounce on a random player (this AoE can be roll dodged) while unleashing a ground AoE at his current location occasionally.
Eliam also proclaims "Take my heel" (a pun on "take my heal" most likely) as he kicks/heavy attacks/staggers the person holding aggro. He will also sometimes send out a shockwave of AoEs that can hurt quite a bit towards the rest of the group.-
At 80%, Eliam summons a side add called Liramindrel who will grant Eliam a white shield that will damage anyone touching it unless they're inside of it. The boss cannot be damaged by most sources of damage (except AoE) from outside of this white shield.
Of course you can ignore the add at a higher risk due to the add's Arrow Spray or the ground AoE Eliam unleashes should groups try to stack on him.
At 50% Health, Eliam summons a second side add called Ihudir who the tank must taunt.
The last boss can be quite overwhelming on the players' senses as multiple mechanics and adds can stack should the group go too fast. Reminiscent of the Dark Souls 3 boss fight, Pontiff Sulyvahn, Prior Thierric summons an untargetable clone that will also attack whoever has the aggro. It will mimic the boss's abilities such as spinning around or heavy attacking. Prior Thierric has cleave so must be pointed away from the rest of the group by the tank.
The first main mechanic Prior Thierric will do will be slamming his sword into the ground to summon ice stalagmite AoEs that will follow the players who must kite these AoEs.
At specific health intervals, Prior Thierric will start introducing new mechanics including moving AoEs, shockwaves similar to Boss 2, exploding AoEs similar to Boss 1 and 2 in addition to AoEs that spawn from any of the four walls in the encounter similar to Veteran Fang Lair's wall of ghosts. These AoEs stagger and damage anyone that hits but their placements are quite predictable.
Prior Thierric also does the same thing as Eliam and sometimes gets the white shield which will be dissipated with the help of Lyranth, the friendly NPC. Red AoEs that are summoned will move around and must be navigated while handling all the aforementioned mechanics at the same time.
Silver Rose Realmshapers also spawn at specific health intervals in pairs and must be cleaved down or taken care of when they're channeling. In the meantime, Prior Thierric will teleport away and attempt to channel which can summon more damage to kill the group. This interrupt on the channel must be prioritized.
Three Crystals before the first main boss encounter must be lit up to open a portal to go to the 1st Secret Boss. The Crystal locations are shown on the player locations in the map below:
A few waves of add spawns will occur with the Wraith of Crows boss spawning at the end with slightly over 2.5 Million Health. The main threat from this boss is the large moving AoE that you must move out of regardless of role.
After defeating the Wraith of Crows, you gain the Crystal Animus Agea buff.
Three Crystals must be lit up to open up a portal to go to the 2nd Secret Boss. One Crystal is in the throne room in the manor after Rogerain the Sly's encounter. The second Crystal is located in a bedroom upstairs while the third Crystal is down in the basement.
A few waves of add spawns will occur with the Spider Daedra boss spawning at the end with 2.5 Million Health. She mainly traps a player in webs which they must be broken free out of. She also summons Lightning AoEs on the ground that blast or move around.
After defeating the Spider Daedra, you gain the Crystal Anima Anya buff:
Three Crystals before the last boss encounter must be lit up to open a portal to go to the 3rd Secret Boss. The Crystal locations are shown on the player locations in the map below:
The last secret boss is a Grievous Twilight with 2.5 Million Health whose main ability is to barrage a specific player. Just like with Lord Warden from the Imperial City Prison dungeon, the tank must block the barrage by placing themselves between the targeted player and the boss.
Defeating this boss grants the group the Crystal Animus Nagaia buff.