Psyonix has just announced that on December 10, Rocket Pass 2 will arrive in Rocket League for free on all platforms, and just like with the first Rocket Pass you can upgrade it to Premium for 10 keys (if you want, of course, we doubt anyone is going to make you).
Rocket Pass 2 features the Artemis Battle-Car, and new customisation item attributes to various Pro Tier items, which includes the "Special Edition" attribute which gives you a 25% chance of unlocking a Special Edition of a Pro Tier item. The Special Edition versions still support paints and such.
For more information, check out the Rocket Pass 2 trailer below.