With Connor taking point, Batman, Batgirl, and Starfire all follow into the Hall of Doom. They find themselves in a literal hallway- one which follows the circumference of the dome-shaped structure.

You all hear heavy footsteps approaching you at an unnervingly even clip- all stepping in exact unison. Focusing, Batman discerns that the sound indicates six sets of footsteps marching towards your party on either side of you. Which seems to indicate a welcoming committee of an even dozen.