In the Mahanirvana-tantra Kali (Troma Nakgmo) is one of the most common manifestations of the primordial Sakti, and Siva praises Her:
"At the dissolution of things, it is Kala (Time) Who will devour all, and by reason of this He is called Mahakala (an epithet of Siva), and since thou devourest Mahakala Himself, it is thou who are the Supreme Primordial Kalika.
Because Thou devourest Kala, Thou art Kali, the original form of all things, and because Thou art the Origin of and devourest all things Thou art called the Adya (primordial) Kali. Resuming after Dissolution thine own form, dark and formless, thou alone remainest as One ineffable and inconceivable. Though having a form, yet art Thou formless; though thyself without beginning, multiform by the power of Maya, thou art the Beginning of all, Creatrix, Protectress, and Destructress that thou art." (4.30-34) 4
Although the debate may be on about this, Mahakala is considered to be enlightened, while other Heruka are considered to be at higher Bodhisattva stage.....