Here is the full list of all 28 Forsaken Remastered achievements worth 1,000 gamerscore.
Complete single player mission 'Fishy' on Total Mayhem without losing a life
Collect all crystals in a single player campaign
Unlock and complete all bonus levels in the single player campaign
Defeat Flygirl
Unlock all playable characters
Discover all secret areas in a single player campaign
Max out on orbital pulsars
Defeat LA Jay
Defeat the Avatar
Defeat the Maldroid
Defeat the Ramqan
Defeat Slick
Defeat Jo
Defeat Sceptre
Defeat Mofisto
Defeat Foetoid
Defeat the Exogenon
Defeat Beard
Defeat Cuvel Clark
Defeat HK5
Defeat the Fleshmorph
Defeat Nim Soo
Defeat Lokasenna
Defeat Ex Cop
Defeat Nutta
Defeat Rex Hardy
Defeat Nubia
Defeat Cerbero