Rocket League October update will come with a new arena, name AquaDome,which messes up the cars under water inside a clear glass urn from which you can see the aquatic fauna, including jellyfish and great white sharks.
You can check what such look these developments in the video attached in this same news. The creators of Rocket League promise to provide more details about this DLC in the coming weeks.
This update is completely free, but we can say that two there will be DLC car payment, Proteus model and the model Triton, at 1.99 euros each.