Here is the full list of all 21 Solstice Chronicles: MIA achievements.
Decrease 30 threat levels in survival.
Use drone bomb ability.
Use drone taunt ability.
Get to level 150 with any class
Use drone scout ability.
Complete the Last Man Standing mission
Defeat Achlys on soldier
Defeat Holt on soldier
Defeat Ker on soldier
Defeat Charon on soldier
Complete the game on any difficulty
Complete the last level on the highest difficulty
Evacuate on the Survival game mode
Fully upgrade one weapon
Fully upgrade five weapons
Fully upgrade all weapons
Fully upgrade class skill tree
Complete survival on M.E.R.C.S. difficulty.
Complete all objectives on survival and evacuate.
Increase 30 threat levels in survival.
Use drone block ability.