The pre-order bundle for Killer Instinct season 3 is available now on the Xbox Store and comes with a pretty decent package. 

Anyone who purchases the bundle at the price of $39.99 will get access to the four launch characters (Tusk, Arbiter, Rash and Kim-Wu) as well as early access to the remaining four, unannounced characters. Season 3 is only scheduled to have 8 characters in total, but it's still unsure if there will be characters like season 2 which were not part of the 8 and received 10 overall. In addition to the characters, you will receive a 2XP boost and 18,000 in KI Gold to use in the store. 

You can pre-order the listing here at the Xbox Store