The skirmish in the Rock of Eternity was a skirmish between Billy and his siblings against Sivana.
Thaddeus asked Billy the champion's name, but he was distracted by a Batarang thrown at him by Freddy. Billy, taking advantage of the distraction, charges the Batarang and stabs it at Sivana and throws him at the wall, knocking Sivana out. Billy and his siblings then try to find the exit as Sivana regains consciousness and goes after them.
To be added