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