Amelyssan

Amelyssan, also known as Amelyssan the Blackhearted or Melissan in disguise, was a priestess and Deathstalker of Bhaal whom that deity entrusted with the task of resurrecting him. Having foreseen his death during the Time of Troubles, Bhaal came to Toril years before the event and mated with mortal females of different races, producing offspring called Bhaalspawn, who were to slaughter each other and fuel his rebirth. Amelyssan's task was to perform rituals that would complete Bhaal's return. However, her own goal, at least towards the end, was to gather all the power of Bhaal's essence released from his children into herself and become a goddess. Posing as a benefactor of the Bhaalspawn under the name Melissan for most people, and gathering together The Five with promises of great power once Bhaal would be resurrected, she manipulated events to the point where nearly all Bhaalspawn were killed, and came close to achieving her goal. However, one Bhaalspawn defeated not only The Five - which suited Amelyssan's plans - but also the prospective goddess herself, beating her in an epic battle in what is officially known as the 'Mana Forge' and gaining control of all of Bhaal's essence for themselves. Having been welded to the essence, her soul was annihilated permanently when it was removed.

Baldur's Gate II
Amelyssan, in Baldur's Gate II: Throne of Bhaal, first appears when the player character teleports from the Pocket Plane into Saradush, posing as a benevolent woman called Melissan. She has been trying to lead some of the citizens to gain audience with Gromnir Il-Khan, a Bhaalspawn who currently controls the city. The guards at the gate refuse to allow entry, and are about to attack the townspeople when the player character's party appears and has to fight the guards. "Melissan" guesses their identity and talks to them after the fight, telling that the city is under siege by the forces of Yaga-Shura, another Bhaalspawn and one of The Five, who wants to destroy all the Bhaalspawn she has gathered there supposedly to keep them safe. Melissan tells the player character that to end the siege, they must first deal with Gromnir, who is only making its problems worse, and then find a way to kill Yaga-Shura, who is a seemingly invulnerable fire giant. When the player character finds a way to the palace, they will see an apparently paranoid Gromnir accusing Melissan of wanting to destroy all the Bhaalspawn, which despite his paranoia will later turn out to be true; other people in the city generally regard Melissan as a well-intentioned meddler. After having killed both Gromnir and Yaga-Shura, the player character will find the city in ruins and all the Bhaalspawn within killed, apparently in spite of the best efforts of Melissan, who has remained unscathed. She tells them that they will next need to kill Sendai and Abazigal, two of The Five and among the most powerful Bhaalspawn, and that she will meet the party in Amkethran.

Once the player character makes it to Amkethran, they will not find Melissan there, but the monk Balthazar will welcome them coolly, saying that she passed by and left. After the player character has gone on to destroy Sendai and Abazigal as well, they will find out that Melissan had a hostile confrontation with Balthazar. When they confront him, he will reveal that he is another Bhaalspawn and member of The Five, though drawn into the group not by Melissan's promises of power but the desire to destroy all of his kind. After he attacks and is killed, all of The Five will be destroyed, and the player character will see a final revelation in the Pocket Plane, which includes the Solar summoning the shades of both Melissan and Bhaal, and revealing that she is really Amelyssan, the most trusted Deathstalker of Bhaal, who was to resurrect him but now only wants the power for herself. After this revelation and a final test, the player character is ready to dissolve the Pocket Plane and move onto the Mana Forge, where Amelyssan waits, in a previously unseen form with a body the size of a small giant's.

The final battle against Amelyssan consists of several fights with no possibility of rest in between. First, Amelyssan will fight and be forced to retreat into the column of energy in the middle of the Forge; then, the player character will need to fight powerful guardians protecting each of the lesser energy sources on the plane, each time cutting one off that one and forcing Amelyssan to fight again. During the different battles she will use different tactics such as summoning Slayer Shadows and abyssal creatures. When she is finally defeated, she will remain alive but unable to fight, and the Solar will appear, declaring the battle over by divine decree. The player character will now have all the essence of Bhaal, and once they decide what to do with it, they will leave the Mana Forge, leaving it to explode, taking Amelyssan with it.