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