We don’t know yet who the ancient enemy is but it isn’t flood.
So it could be forerunners, precursors or something new.
In the 5th halo CE anniversary terminal there is an unknown vessel that crashed on alpha halo.
Don’t think its covenant because its 3000 years after the firing of the halo array.
So do you think the unknown vessel is related to the ancient enemy?
Video link for the terminal - http://
www.youtube.com/watch?v=8Zj68_95Jnk