Here is the full list of all 30 Killer Instinct Classic achievements worth 1,000 gamerscore.
You defeated Eyedol with Glacius
You won 40 Matches with Riptor.
You won 40 Matches with Orchid.
You spent 400 credits!
You won 40 Matches with Glacius.
You won 40 Matches with Fulgore.
You won 40 Matches with TJ Combo.
You won 40 Matches with Spinal.
You humiliated every character in the game
You won 40 Matches with Saberwulf.
You won 40 Matches with Chief Thunder.
You won 40 Matches with Cinder.
You won 40 Matches with Jago.
You got a Perfect in Arcade with Spinal, Riptor and Sabrewulf
You performed a humiliation!
Perform an ultra
Defeat Eyedol with Chief Thunder
Defeat Eyedol with Cinder
Defeat Eyedol with Fulgore
Defeat Eyedol with Jago
Defeat Eyedol with Orchid
Defeat Eyedol with Riptor
Defeat Eyedol with Sabrewulf
Defeat Eyedol with Spinal
Defeat Eyedol with TJ Combo
Defeat Eyedol with all characters
Defeat Eyedol using only one credit
Perform an ultra with every character in the game
See all Victory Animations and Endings
Win a match in every arena