Killer Instinct: Season 2 begins in mid-October, adding eight new playable characters to the fighter's roster.
Killer Instinct is being re-released on October 15 as "Killer Instinct: Season 2", Microsoft announced at gamescom 2015. The new version has a "completely revamped interface" as well as enhanced game modes and an expanded roster.
You can grab the new characters as DLC for the original in the $20 Combo Breaker Pack, or fork out $40 for the Ultra Edition, which includes the full, stand-alone game, all the new characters as they release, plus extra goodies like costumes and accessories. You can also buy individual characters for $5 each.
In any case, you won't get the full set of eight new characters immediately. The first two, TJ Combo and Maya, will be available October 15, but the remaining six will release at a rate of one per month.
One last point: if you pre-purchase Killer Instinct: Season 2 Ultra Edition between September 23 and October 14, you'll get early access to TJ Combo.