This feature is part of the March 2014 paid 'Season One' DLC.
Ending: Evil side
Ultra your sixth opponent, but not your seventh opponent.
Ending: Good side
Do not Ultra your sixth or seventh opponent.
Ending: Neutral
Ultra both your sixth and seventh opponents.
Hidden remixed classic themes
If you start a match and have both players do nothing, after around 10 seconds, a remixed version one of the character's classic themes will play. The theme that plays corresponds with what character's stage you are on. Doing any action will cause the music to fade back into the regular theme.
Shadow Jago
To unlock Shadow Jago, you must unlock the three endings of a character, then play Arcade mode in Medium or higher difficulty. Do not lose any fight. After defeating Fulgore, you are taken to fight Shadow Jago. Note: Shadow Jago is always set to Kyle Difficulty. It is ok to lose against him.
Various Achievements
Complete the following achievements to unlock Xbox Live Gamerscore points.
Achievement
How to unlock
Battle-worn Glacius (10 points)
Win 20 ranked matches with Glacius.
Battle-worn Jago (10 points)
Win 20 ranked matches with Jago.
Battle-worn Orchid (10 points)
Win 20 ranked matches with Orchid.
Battle-worn Sabrewulf (10 points)
Win 20 ranked matches with Sabrewulf.
Battle-worn Sadira (10 points)
Win 20 ranked matches with Sadira.
Battle-worn Thunder (10 points)
Win 20 ranked matches with Thunder.
Black Belt (10 points)
Complete 32 Dojo Lessons.
Competitive Glacius (5 points)
Win a Ranked Match as Glacius.
Competitive Jago (5 points)
Win a Ranked Match as Jago.
Competitive Orchid (5 points)
Win a Ranked Match as Orchid.
Competitive Sabrewulf (5 points)
Win a Ranked Match as Sabrewulf.
Competitive Sadira (5 points)
Win a Ranked Match as Sadira.
Competitive Thunder (5 points)
Win a Ranked Match as Thunder.
Friendly Glacius (10 points)
Win an exhibition match vs a friend as Glacius.
Friendly Jago (10 points)
Win an exhibition match vs a friend as Jago.
Friendly Orchid (10 points)
Win an exhibition match vs a friend as Orchid.
Friendly Sabrewulf (10 points)
Win an exhibition match vs a friend as Sabrewulf.
Friendly Sadira (10 points)
Win an exhibition match vs a friend as Sadira.
Friendly Thunder (10 points)
Win an exhibition match vs a friend as Thunder.
General Apprentice (10 points)
Reach 30 General Fight Titles.
General Master (10 points)
Reach 60 General Fight Titles.
General Novice (10 points)
Reach 10 General Fight Titles.
Glacius Apprentice (20 points)
Reach 80 Fight Titles with Glacius.
Glacius Chosen One (10 points)
Complete 2000 matches as Glacius.
Glacius Master (10 points)
Reach 150 Fight Titles with Glacius.
Glacius Novice (20 points)
Reach 30 fight titles with Glacius.
Glacius' Armor (10 points)
Absorb a hit with Glacius' Ice armor while in Instinct Mode.
Glacius' Endurance (10 points)
Defeat 10 opponents in one Survival as Glacius.
Glacius' Matchups (15 points)
Defeat 6 different characters in online matches as Glacius.
Hyper Trials! (10 points)
Complete 20 Trials.
Jago Apprentice (20 points)
Reach 80 Fight Titles with Jago.
Jago Chosen One (10 points)
Complete 2000 matches as Jago.
Jago Master (10 points)
Reach 150 Fight Titles with Jago.
Jago Novice (20 points)
Reach 30 fight titles with Jago.
Jago's Endurance (10 points)
Defeat 10 opponents in one Survival as Jago.
Jago's Matchups (15 points)
Defeat 6 different characters in online matches as Jago.
Monster Trials! (10 points)
Complete 100 Trials.
Orange Belt (10 points)
Complete 16 Dojo Lessons.
Orchid Apprentice (20 points)
Reach 80 Fight Titles with Orchid.
Orchid Chosen One (10 points)
Complete 2000 matches as Orchid.
Orchid Master (10 points)
Reach 150 Fight Titles with Orchid.
Orchid Novice (20 points)
Reach 30 fight titles with Orchid.
Orchid's Endurance (10 points)
Defeat 10 opponents in one Survival as Orchid.
Orchid's Jaguar (10 points)
Hit an opponent with a Jaguar while in Instinct Mode with Orchid.
Orchid's Matchups (15 points)
Defeat 6 different characters in online matches as Orchid.
Sabrewulf Apprentice (20 points)
Reach 80 Fight Titles with Sabrewulf.
Sabrewulf Chosen One (10 points)
Complete 2000 matches as Sabrewulf.
Sabrewulf Master (10 points)
Reach 150 Fight Titles with Sabrewulf.
Sabrewulf Novice (20 points)
Reach 30 fight titles with Sabrewulf.
Sabrewulf's Claws (10 points)
Perform 10 points of chip damage while in Instinct Mode with Sabrewulf.
Sabrewulf's Endurance (10 points)
Defeat 10 opponents in one Survival as Sabrewulf.
Sabrewulf's Matchups (15 points)
Defeat 6 different characters in online matches as Sabrewulf.
Sadira Apprentice (20 points)
Reach 80 Fight Titles with Sadira.
Sadira Chosen One (10 points)
Complete 2000 matches as Sadira.
Sadira Master (10 points)
Reach 150 Fight Titles with Sadira.
Sadira Novice (20 points)
Reach 30 fight titles with Sadira.
Sadira's Endurance (10 points)
Defeat 10 opponents in one Survival as Sadira.
Sadira's Matchups (15 points)
Defeat 6 different characters in online matches as Sadira.
Sadira's Web Trap (10 points)
Trap an opponent with a web trap while in Instinct Mode with Sadira.
Sparring Glacius (5 points)
Win a versus match as Glacius.
Sparring Jago (5 points)
Win a versus match as Jago.
Sparring Orchid (5 points)
Win a versus match as Orchid.
Sparring Sabrewulf (5 points)
Win a versus match as Sabrewulf.
Sparring Sadira (5 points)
Win a versus match as Sadira.
Sparring Thunder (5 points)
Win a versus match as Thunder.
Stylish Glacius (10 points)
Purchase a skin for Glacius.
Stylish Jago (10 points)
Purchase a skin for Jago.
Stylish Orchid (10 points)
Purchase a skin for Orchid.
Stylish Sabrewulf (10 points)
Purchase a skin for Sabrewulf.
Stylish Sadira (10 points)
Purchase a skin for Sadira.
Stylish Thunder (10 points)
Purchase a skin for Thunder.
Supreme Glacius (10 points)
Earn a supreme Victory in an online match as Glacius.
Supreme Jago (10 points)
Earn a supreme Victory in an online match as Jago.
Supreme Orchid (10 points)
Earn a supreme Victory in an online match as Orchid.
Supreme Sabrewulf (10 points)
Earn a supreme Victory in an online match as Sabrewulf.
Supreme Sadira (10 points)
Earn a supreme Victory in an online match as Sadira.
Supreme Thunder (10 points)
Earn a supreme Victory in an online match as Thunder.
Survival Glacius (5 points)
Win a survival match as Glacius.
Survival Jago (5 points)
Win a survival match as Jago.
Survival Orchid (5 points)
Win a survival match as Orchid.
Survival Sabrewulf (5 points)
Win a survival match as Sabrewulf.
Survival Sadira (5 points)
Win a survival match as Sadira.
Survival Thunder (5 points)
Win a survival match as Thunder.
Thunder Apprentice (20 points)
Reach 80 Fight Titles with Thunder.
Thunder Chosen One (10 points)
Complete 2000 matches as Thunder.
Thunder Master (10 points)
Reach 150 Fight Titles with Thunder.
Thunder Novice (20 points)
Reach 30 fight titles with Thunder.
Thunder's Endurance (10 points)
Defeat 10 opponents in one Survival as Thunder.
Thunder's Matchups (15 points)
Defeat 6 different characters in online matches as Thunder.
Thunder's Spirit Dash (10 points)
Do a dash while in Instinct Mode with Thunder.
Tiger's Fury (10 points)
Healed 10 health points while in Instinct Mode with Jago.
Triple Trials! (10 points)
Complete 3 Trials.
ULTRA TRIALS! (10 points)
Complete 200 Trials.
White Belt (10 points)
Complete 5 Dojo lessons.
Various Characters
Below is a list of ALL the characters that are currently available from 'Season One' DLC. 'Season Two' DLC is rumored but expected to bring 8 more characters in late 2014.
Fulgore
Fulgore will be unlocked after an automatic download in March 2014, as part of any Paid DLC Pack.
Glacius
Glacius can only be downloaded via the Paid DLC.
Jago
Jago is the only character who is always available for free in the 'Round One Pack' — as part of Microsoft's free-to-play model — when you download Killer Instinct.
Orchid
Black Orchid can only be downloaded via the Paid DLC.
Sabrewulf
Sabrewolf can only be downloaded via the Paid DLC.
Sadira
Sadira can only be downloaded via the Paid DLC.
Shadow Jago
Only available as an Exclusive DLC Character download code, that you can get by buying the Day One 12-Month Xbox Live Membership Card.
Spinal
Spinal will be unlocked after an automatic download in January 2014, as part of any Paid DLC Pack.
Thunder
Chief Thunder can only be downloaded via the Paid DLC.
Arcade Mode...