Here is the full list of all 12 Gunjack achievements.
Mission 1-10 completed with at least a 2 star rating
100% enemies killed in 3 missions
Mission 1 completed
3 stars earned in both Bonus Missions
‘Master’ score earned for one mission
100 Power ups used.
Destroy 1.000 asteroids in Bonus missions
Missions 11- 20 completed with at least a 2 star
5000 Enemies killed
50 Stars earned
Mission 20 completed with 3 stars
“Master” score earned for all missions.