Here is the full list of all 20 Fusion: Sentient achievements worth 200 gamerscore.
Finish training at the Luna Academy
Leave the Order planet to find Hyperion
Save The Dominion and Order Forces on Killian's Rest
Discover the relationship between Paeon, Hyperion, and yourself
Complete the campaign
Defeat 300 opposing sentients
Earn your first roster upgrade
Own at least one of each unit type
Complete 20 missions in the Ghost Fleet
Defeat 20 opposing sentients with a shotgun
Destroy more than one enemy unit with a single attack
Complete 10 missions by recovering all artifacts
Stun all opposing sentients on a level
Complete 10 missions by destroying all opposition
Have 50,000 Credits in the bank at one time
Sell or auction off at least 200,000 Credits of merchandise
Complete a mission on the final planet with a common unit in your team
Knock back an enemy while the enemy is being knocked back towards the unit
Equip and use a legendary melee weapon
Reach level 60 with a unit