Sub Zero

Sub Zero is the fifth episode/circuit in Angry Birds Go! (Was Announced) Currently, this is the last episode/circuit, but this may change as there is rumored to be a fifth episode/circuit in the making since no one has won the cake yet.

Angry Birds was announced on Facebook:

Things are about to get really frosty in Angry Birds Go! We have a free new episode coming soon, so stay tuned! http://rov.io/downloadabgo

Karts
Unknown

Trivia
The Champion Chase Characters is unknown