People who have watched Mixnine will be familiar with these girls and one of the members in particular. Black Mamba is the upcoming seven member girl group from ONO Entertainment.

Their line-up consist of:
Yongchae
Ayoung: former Happy Face trainee from Produce 101
Huiwon
Yesol
Subin
Jungmin: former Yama & Hotchicks trainee from Produce 101
Bora

They haven't announced a debut date yet, but ONO recently opened up a Youtube channel for Black Mamba and on their official page it says the group is coming soon.