Here is the full list of all 33 Gunslinger Nova achievements.
Give up in battle.
Complete Campaign Mode levels 1-40.
Complete all stars for levels 1-10.
Complete all stars for levels 11-20.
Complete all stars for levels 21-30.
Complete all stars for levels 31-40.
Complete all stars.
Complete all 40 waves in Endless Mode.
Purchase Slow Motion.
Purchase Force Wave.
Purchase Shield.
Purchase Gun Ring 2.
Purchase Rapid Blaster.
Purchase Medium Blaster.
Purchase Basic Launcher.
Purchase Phase Beam Cannon.
Purchase Burst Blaster.
Purchase 8-Way Blaster.
Purchase Salvo Launcher.
Purchase Scatter Beam Cannon.
Purchase Small Steel Slug.
Purchase Small Plutonium Slug.
Purchase Small Fusion Warhead.
Purchase Medium Radium Slug.
Purchase Medium Plasma Bolt.
Purchase Medium Fission Warhead.
Purchase Missile Random Enemy.
Purchase Missile Closest Enemy.
Purchase Missile Random Portal.
Purchase Missile Closest Portal.
Purchase Proton Beam.
Purchase Antimatter Beam.
Purchase Nova Beam.