The Tenth Doctor stated that he had not seen anything like it since the Old Times, and that it was capable of "doing anything"; breaking down dimensional barriers, resurrecting long dead worlds and civilisations, and saving another's life. It could also destroy individuals or sometimes entire planets. The Crimson Hand used it as a source of their powers, and used the relic to destroy the Skith Homeworld, and to rid Majenta Pryce's homeworld of poverty. After Majenta used the Manus Maleficus to destroy the other four members of the Crimson Hand, the Maleficus fell back into the Morass; but not before the Doctor used it to save Majenta and send her and Zed to a new world.
In order for the Maleficus to work, it required five individuals using it; otherwise interacting with the device could be fatal, except apparently for Time Lords such as the Doctor. (COMIC: The Crimson Hand)