Thralls

Thralls are the minions of the Sorcerer before their imprisonment in the Librum Claustrum, and are the members of their party. There are 14 Thralls, however only a few of them can join you in one game. In the tutorial level you'll eventually be able to summon 3 of them, and later you can go through the Catacombs to find means of summoning 3 more for a total of 6 Thralls.

There is also a 15th party member. The first way to summon a new Thrall in the Catacombs is by sacrificing an enchanted Puppet, but you can instead have the Puppet join you as a Thrall. This is the only chance you have to add the Puppet to your summons.

Each Thrall can only equip certain items, but they can all equip runes. Also, Thralls still gain EXP even if they're not in the party or are Knocked Out.