Here is the full list of all 26 Chasm: The Rift achievements.
Kill the level 4 boss
Kill the level 8 boss
Kill the level 12 boss
Kill the level 16 boss
Kill the level 3 boss of the expansion pack
Spend three minutes trying to get past the gate in the first Egypt level
Spend three minutes trying to get past the gate in the first level of the expansion pack
Find all the secret rooms and hidden items
Die for the first time
Use the OP Mega Destroyer for the first time
Get killed by the fan on level 4
Get killed by an environmental hazard like poisonous water, lava, or a trap
Get killed by your own weapon
Shoot off a total of 50 enemy limbs
Gib enemies into a total of 500 chunks
Find all the unique powerups, including Invisibility, the Reflector, and the Chojin Mask
Destroy 20 light sources (light bulbs, etc.)
Blow up at least four enemies with one shot
Kill an enemy with the Reflector
Beat the game
Beat the game on hard
Beat the game without dying
Beat the game in 90 minutes or less
Beat the game using only your first weapon
Beat the game on hard without dying using only your first weapon
Watch the credits at the end of the game