Killer Instinct is said to have received a 6.8GB update that adds new fighter Fulgore and story mode, along with a host of gameplay tweaks and achievements.
Fulgore is the last character of Killer Instinct's first season, and as you can see, comes with a range of customisation options.
Killer Instinct Central also has a list of Fulgore-related achievements that go as follows:
Fulgore Novice (20)
You have reached 30 fight titles with Fulgore!
Battle-worn Fulgore (10)
You have won 20 ranked matches as Fulgore!
Stylish Fulgore (10)
You have purchased a skin for Fulgore!
Supreme Fulgore (10)
You have earned a Supreme Victory in an online match as Fulgore!
Fulgore’s Endurance (10)
You have defeated 10 opponents in one Survival as Fulgore!
Fulgore’s Matchups (15)
You have defeated 6 different characters in online matches as Fulgore!
Fulgore Chosen One (10)
You have completed 200 matches as Fulgore!
Sparring Fulgore (5)
You have won a versus match as Fulgore!
Friendly Fulgore (10)
You have won an exhibition match vs a friend as Fulgore!
Survival Fulgore (5)
You have won a survival match as Fulgore!
Fulgore Master (10)
You have reached 150 Fight Titles with Fulgore!
Fulgore Apprentice (20)
You have reached 80 Fight Titles with Fulgore!
Competitive Fulgore (5)
You have won a ranked match as Fulgore!
Fulgore’s Devastation Beam (10)
You hit an opponent with the Devastation Beam while in Instinct Mode
According to Microsoft developers in this PlayXBLA stream, Killer Instinct's second season will come with a "really nasty" boss character, and that a release date for the next round of new content will be confirmed soon.