"Nettie said that only a Shadow Man, or something more powerful, could release a Dark Soul from a Govi. This is bad - real bad..."
-Shadow Man when seeing the remains of a Govi in the Experimentation Rooms.
Govi are containers which the Loa sisters had used to seal up the Dark Souls in ancient times, so that no form of evil could use it for themselves (i.e. Legion). Sealed by the most powerful voodoo, nether Bokor nor Mambo had proven sucessful in opening one to release the Dark Soul within. Mama Nettie had tried to do so, only to fail as well. As Shadow Man, Mike is able to break open a Govi, and eventually the rest of them with a simple blast from his Shadow Gun. Legion is believed to be just as capable, as some of the Dark Souls located in the Asylum are shown exposed, or already inside the bodies of Trueforms.