Andy mentioned 12 days ago that Rocket League's AquaDome update (it adds an 'AquaDome' and 'AquaCars', natch) would be arriving in October, and now that we're in October, that update has suddenly appeared. You want to battle other cars in a big game of football under the sea, right? Of course you do, so get a load of update 1.24's patch notes, which break down all the stuff that's just been elbowed in.
The headline, naturally, is that aforementioned AquaDome, and if I type 'AquaDome' enough times maybe it will eventually sound like a real word. That soggy dome has been added to all playlists as a new arena, while two new, underwater-themed cars are available as DLC. One's called Proteus; the other's named Triton, and looks like this:
You'll be pleased to hear that "updated 'Cosmic' and 'Octagon' arenas have been added to the 'Rocket Labs' playlist" too, while there are bunch of new car parts, and tweaks/fixes to the underlying game.
To know exactly what's just been added, changed, or shifted about a bit in Rocket League, have a read of the whole patch notes here.