Here is the full list of all 12 Outland achievements.
Complete the full game (Individual)
Complete any Co-op Challenge Room (General)
Kill 20 enemies in a row with only 1 health left (Individual)
Complete any Arcade Chapter below the target time (General)
Collect 1,000,000 Doubloons (Single Player only)
Defeat any boss without taking damage (General)
Collect all Marks of the Gods (Single Player only)
Destroy six enemies with one Beam Shot (Individual)
Smack a bomb so that kills two or more enemies (Individual)
Destroy a Spider using spikes (General)
Collect 10 Marks of the Gods (Single Player only)
Destroy an enemy using a Kamikazer (General)