The Arbiter Add-on for Killer Instinct has 14 achievements worth 150 gamerscore.
Reach 150 Fight Challenges with Arbiter
Win 20 ranked matches with Arbiter
Complete 200 matches as Arbiter
Reach 80 Fight Challenges with Arbiter
Win a Ranked Match as Arbiter
Defeat 6 different characters in online matches as Arbiter
Earn a supreme Victory in an online match as Arbiter
Win an exhibition match vs a friend as Arbiter
Win a versus match as Arbiter
Parry 5 attacks while in Arbiter's Instinct Mode
Defeat 10 opponents in one Survival as Arbiter
Reach 30 Fight Challenges with Arbiter
Unlock a color for Arbiter
Win a survival match as Arbiter