Residing in Mortis' Courtroom, Mortis is the final boss of the Sea of Shadows region. To access Mortis' Courtroom, complete the quest Across the Sea of Souls and give 1 Coin to the Ferryman to transport you across the Sea of Souls. The level of Monsters will scale to the highest-level player in the group and the difficulty will scale to the number of players.
During phase I of the battle, players must defeat a stationary Skeledragon located at the end of the dungeon. Mortis' Bodyguard will also appear to challenge you in battle.
Skeledragon and Mortis
Killing Skeledragon will initiate phase II, and the arrival of Skeledragon and Mortis. Mortis' Bodyguards will continue to enter the courtroom.
The team goal is to defeat Mortis before too many Hateful Soul enter the center seal. If the count surpasses 1000, all player in the arena will face an inevitable death and Mortis revives complete health.
Malicious soul (6 soul count) - fast moving, low health
Malevolent soul (43 soul count) - slow moving, high health
Negation puddles will drop within the courtroom; players in the puddle will not be able to use any skills, and must walk outside the puddle before being able to use skills.
Stepping into the center seal will cause continuous andermagic damage and slows movement.
Teams must balance players between attacking Mortis and preventing high number of souls from reaching the center seal.
Trivia
Mortis is the fabled Lord of the Dead, first appearing in R084.
: Cap of Death, Amulet of Death, Starlight, Enigma
: Death Mask, Chain of Death, Predator, Beast
: Helmet of Death, Seal of Death, Cloaked Wrath, Justice
: Horror Mask, Seal of Death, Avenger, Mechanicum
Negation puddles will drop within the courtroom; players in the puddle will not be able to use any skills, and must walk outside the puddle before being able to use skills. 
Cap of Death
Death Mask
Helmet of Death
Horror Mask
Amulet of Death
Seal of Death
Predator
Cloaked Wrath
Avenger
Enigma
Beast
Justice
Mechanicum
