Serapis

Serapis, is a Graeco-Egyptian god of the Underworld and fertillity. He is also the main deity of Alexandria.

Biography
In ancient times, Serapis was originally a minor village god who no one had even heard of. However, when Ptolemy took over rule of Egypt, he decided to find a new supreme god for Egypt and found Serapis' statue. Ptolemy had Greek and Egyptian priests perform auguries and incantations to make Serapis the new supreme god of Egypt which made him incredibly powerful. As more people believed in him, Serapis grew more and more powerful, draining and replacing the other gods. Serapis overthrew Osiris, Zeus and Hades and took control of the Underworld. Upon doing so, Serapis transformed Cerberus into a staff that allows him to control past, present and future. He bound Isis and forced her to serve him and be his queen. However, making Serapis a major god wasn't enough for Ptolemy and he tried to turn himself into a god as well, but this backfired and his family was cursed. The Ptolemaic dynasty grew weaker and weaker until it finally fell to the Romans when Cleopatra committed suicide. Serapis and his cult were forgotten and eventually he fell into a state of hibernation while his staff became a statue and was split into three parts with one eventually ending up in the Metropolitan Museum of Art, another in an antique shop and the last in Brooklyn House. With Serapis gone, the Greek and Egyptian gods regained control of their domains.

The Staff of Serapis
After getting the Book of Thoth, Setne began experimenting with combining Greek and Egyptian magic. To this end, he used the Book to awaken Serapis to see how the magicians and demigods would react to him. Serapis seemed to think Setne wanted to control him but lacked the power, but it was actually just a test of his new abilities and his enemies capabilities. Serapis awakened the three pieces of his staff and they began to come together and make their way to Rockaway Beach where Serapis began building a replica of the Lighthouse of Alexandria to draw the other gods to him like a beacon and feed on their essences to become more powerful and take over the universe. His staff's attempts to reunite and reach him draw the attention of Annabeth Chase and Sadie Kane who team up to stop him. Despite their best efforts, the three pieces of his staff merge together and enter the maelstrom in the apartment building Serapis is cannibalizing to form his lighthouse. As the maelstrom carries the staff towards him, Sadie transforms into a kite to stop it and orders Annabeth, protected from the maelstrom by a force field, to distract Serapis. Annabeth is able to get his attention, causing him to freeze the maelstrom and face off with her. The distraction allows Sadie to drop one of Walt's camels on top of the staff and pin it down so that it can't reach Serapis. Serapis comes to believe that Annabeth is there to be his new high priestess and she distracts him by getting him to explain about his past and what he is up to while Sadie, unnoticed by the god, prepares a spell. Sadie is shocked to learn about Setne's involvement in Serapis' return, but manages to bind him with a spell before he can get to his staff. However, Serapis easily breaks free of the bindings, enraged that Sadie tried to bind and name him and turns his recovered staff on the two girls. Sadie manages to collapse the building on top of Serapis, burying him for a short time, but he eventually manages to break free, intent on killing Sadie and Annabeth and using them as a gateway to draw Athena and Isis into the world, Athena to consume and Isis to enslave. However, Athena returns Annabeth's Yankees Cap and Annabeth realizes they need to destroy the dog head on his staff representing the future to destroy him. While Annabeth uses the cap to sneak up on an oblivious Serapis and his staff, Sadie stalls him with a bluff that she has cast a death link on him that will destroy him if he kills her. Serapis hesitates, but eventually sees through the bluff and goes to attack her. However, Annabeth has reached the staff by that point, removes her celestial bronze dagger from it and kills the dog's head. Doing this destroy Serapis' staff and his future without which he's nothing. As Serapis yells that they will never attain the crown without him and will all perish, his staff turns into a fireball that consumes and destroys him before extinguishing itself. Sadie and Annabeth realize from Serapis told them that Setne is trying to use the crown of Ptolemy to become immortal and that Serapis was likely just a test of their capabilities like the petsuchos was of Carter and Percy's a few weeks before.