User blog comment:MetalMickey272/Game Idea!: SONIC ARENA/@comment-3295259-20110622054729/@comment-17720060-20110622193237

Ix and the Nocturnus were left to stay imprisoned in the Twilight Cage. You can tell since the heroes were the only ones to leave and Ix teleported somewhere else so that he could close the portal on Sonic and his team (refer to Shade's quote after Ix teleported).