Here is the full list of all 27 Sky Mercenaries achievements.
Visit all Hangar Areas
Unlock first Air Sniper Player Skill
Complete all Earth C-1 Stages
Change Firemodes over 20+ times in one Stage
Finish the first Stage
Reach Ship Level 2
Change Firemode to incomming Bullet Color
Kill 1000+ Enemies
Collect 1000 Powerups
Collect 100 000+ overall Credits
Play one of your Ships to ShipLevel 10+
Upgrade your Ship 10+ times
Finish a Stage at 150% Difficulty or harder
Unlock first Defense Ace Player Skill
Unlock first DroneMaster Player Skill
Kill 10000+ Enemies
Absorb 200+ Bullets in one Stage
Test 10+ different Ship, Pilot, Drone and Upgrade Combinations
Become a Defense Ace - Unlock all John Hawk Skills
Become a Air Sniper - Unlock all Lea Striker Skills
Become a Drone Master - Unlock all Bill Riddim Skills
Complete all Stages on all Planets
Install all Ship upgrades up to lvl 25
Create a new 100+ objects stage
Share a unique created stage
Download and play a user created stage
Finish a mission stage in Hardcore mode