It is a weapon that is a fragment from another realm, which Necrid broke off and brought with him when he returned to this world. It is something never before seen in this world: a physical manifestation of the same energy contained within the Soul Edge. This substance is both comforting and familiar to Necrid, which is why Maleficus is such a well-suited weapon for him.
Maleficus, much like Soul Edge, is a shapeshifting weapon, composed entirely of a green and black-colored energy construct (pink when using the 2P costume). It takes on a myriad of forms that give Necrid a myriad of options to use, which of includes a long sword, twin blades, a flexible sword, an axe and an orb form.