Iirc, it never was a mode. The game was just a originally a CTF style game, and some files were left over making people think it was a mode, or something like that.
That what I think I remember hearing, but not sure.
Even if it was never actually a mode, it sounded interesting. Definitely would have added a bit more variety to online.
Sounds like something like, collect the flag from a starting point, then try to hold onto it. You gain more points the longer you keep the flag. Hitting someone with a super makes them drop the flag. Game's over after time runs out/point limit is reached.