Bruce barely had time to register surprise at Ross' apparent drastic shift in tactics before he had to make a move. Rather than attempt to regain his balance, Bruce made the floor immediately beneath him cave entirely so that he fell downward and outside of the blade's reach. That done, he caught himself from falling deeper by jamming his sheath between the walls of the hole, and redoubled the efforts of his earthborn ally. 
Bruce pondered what the sudden shift meant. And he'd noticed how Ross' skin had changed somehow. Did his spike in speed mean he'd shed his stone skin completely, or did he change the material? The latter seemed more likely. Bruce couldn't help but smile a bit despite the intensity of the fight- Ross was keeping his word to give Bruce as much variety as possible. 
Thinking done, Bruce carved out a chute in the side of the wall that led back up to the surface behind Ross, and swung his body on his sheath to launch himself up through it, collapsing the material down behind him. Once he was up, his colossus had torn past Ross' granite platform, and Bruce set about adding a spike to the chain left around its base on the side opposite Ross. To avoid becoming predictable with only dodging, and since he didn't know Ross' full speed yet, Bruce also called his sword back from its sheath, settling himself to observe.