German print magazine PC Games is reporting about the magic system. While the magazine will be available at Wednesday, subscribers already have it and people are already discussing the details in the German forum. So I thought I should give you a summary as well.
We already know that the magic will be Voodoo. As it seems, there will be no dedicated mage class in the game. Does not fit the concept anyway. It is a pirate game and you are supposed to be a pirate. And a good little pirate fights with muskets and/or cutlasses! Magic has been reduced to a support role, similar to the dirty tricks. It may also open new solutions for quests but based on what is currently known, I seriously doubt that you will be able to play a pure mage, i.e. get through the game with reasonable effort only relying on magic and without using conventional weapons.
The option to learn magic is presented to you on the first island after the tutorial. There, you will find two factions opposing each other: The Inquisition and the natives. You will have to team up with one of them (no, there will not be a third faction to choose from). If you join the Inquisition, you get access to firearms. If you join the natives, you get access to Voodoo.
Voodoo magic in the game is governed by the attribute "Black Magic" and consists of these elements:
You can make real Voodoo dolls of your enemies. You will need something of them (like hair) and some other ingredients (herbs, animal teeth, etc.) which you can either collect yourself or buy from the local Voodoo dealer. The dolls are made at an altar and allow you to control the people they represent. This is used at certain, pre-defined points in the game as an alternative solution for problems. There are also curse-dolls which weaken someone. But like all Voodoo magic, it does not deal direct damage. Dolls disappear after they have been used.
Sceptres work similar to wands in D&D games like NWN. They have a specific function that can make your life easier. They can be used multiple times but like the dirty tricks, they have a cooldown period. Sceptres also do not directly damage an opponent but provide support for certain situations (causing fear, help with stealing, freezing time etc.).
This is a bit of a mystery at the moment. Apparently, this was mentioned in "GameStar TV" (a video stream for subscribers/payers of the German magazine GameStar). They discovered this in the character screen as a skill. But it was not available to them and they did not know what it would do. I am not even entirely certain it is really a part of Voodoo but it seems plausible, of course.