Here is the full list of all 26 Nebula achievements.
Hunt 500000 of space invaders.
Inflict 10 million damage.
Reach maximum level for both rocket launchers in one mission.
Reach maximum level for both double barrels in one mission.
Reach maximum level for minimum two lasers in one mission.
Complete two first missions in a game.
Finalize Metalox_SR500 and Garou_x2 missions
Finalize Tartarus_9x8 mission.
All missions completed
Reach maximum level for Shield in one mission.
Reach maximum level for Health Steal during one mission.
Reach maximum level for Luck in one mission.
Reach maximum level for at least two guns in one mission.
Reach maximum level for shooting satellites in one mission.
Reach maximum level for freezing EMP and plasma cannon during one mission.
Reach maximum level for freezing blades and space mines during one mission.
You deserve more fire power.
Reach maximum level for YY Ball and at least one of the plasma turrets during one mission.
Reach maximum level for all Laser type weapons in one run.
Reach maximum level for: Plasma Torch, Force Field, Space Mines, Freezing EMP, Gravitons, Burning EMP weapons in one run.
Reach maximum level for: Freezing Blades, Heavy Rocket, SpaceMines, Regular Rockets, Freezing Rockets weapons in one run.
Unlock all weapons.
Unlock all power-ups in Hangar.
Hunt more than 20k enemies in one run.
Inflict more than 1 million damage in one run.
Finalize extra mission.