Here is the full list of all 12 Lara Croft and the Guardian of Light achievements worth 200 gamerscore.
Collect all 10 red skulls in any single level
Complete any level-specific Reward Challenge
Play Co-op mode
Catch Totec with the grapple while he is jumping over a death fall
Reflect an enemy's projectile back to him using Totec's shield
Kill 3 enemies with one bomb
Jump from Totec's shield while he is jumping
Activate all of the spikes at once in the Spider Tomb spike field
Earn the top score objective in any level
Collect all relics, artifacts and weapons