Bwonsamdi is a powerful Loa, whose domain primarily revolves around the souls of dead trolls.
The heart of his power in the mortal world is the Necropolis; a massive temple situated deep in the Nazmir swamp on the island of Zandalar. This temple is the main -- though certainly not the only -- conduit to the Loa's realm of power; a sprawling troll city of the dead known as De Other Side.
As the city grows ever more populous, so do Bwonsamdi's powers grow in turn.
Involvement
Bwonsamdi is the patron deity of Gan Jedi; granting the shadow hunter all his magical powers in return for the occasional 'favour'. The Loa has not been shy for sweeping in to claim the passing souls of more powerful foes the party have slain, and he has even offered strange deals in return for them seeking out particularly strong creatures so that he may take them too.
But what is the worst that could come out of making deals with a god of the dead?