When Devas prayed to save them from Shumbh, Nishumbh, Paravti came there to bath in Ganga, she asked them ,whm are they praying to? At that time Ambika came out from her, told her they are praying to me. She was fair, 8 handed ( After killing Mahishasur 18 handed form of Durgama had merged in Parvati). Due to that Paravti turned dark.
This Ambika killed Shumbh, Nishumbh. From her Ma Kali appeared to kill Chanda, Munda & helped, Chandika, appearingg from Ambika, in killing Raktabeeja. Dhumralochan was killed by just " Hum" kar of Ambika. Even other Devas shaktis like Brhmani, Aindri, Varahi, Narsimhi, Koumari etc came to help Ambika, they all merged in her before killing Shimbh, when he told her I am fighting alone & you are fighting with your army.