Here is the full list of all 63 Gunslugs achievements.
Complete bootcamp
Complete mission 1.1
Complete mission 1.2
Collect 75 coins
Grab a new weapon
Make a chopper crash
Change the tune using a jukebox
Kill 10 guys in a mission
Collect 100 coins
Find the voodoo priest
Blow up 2 dudes at once
Air kill a dude
Complete mission 1.3
Kill 5 guys from cover
Complete mission 2.1
Score 500 points
Rescue Sly Rocko
Collect 125 coins in one game
Rescue Willis KiYay
Drive a tank
Complete mission 2.2
Find "a" princess
Kill 20 guys
Take a jetpack ride
Locate the arcade !
Kill 10 guys with grenades
Complete mission 2.3
Collect 150 coins
Score 1000 points
Grab energy drink
Chain explosion of 2
Complete mission 3.1
Blow up 4 dudes at once
Kill 50 guys in one mission
Complete mission 3.2
Get your train ticket and ride.. or run
Score 2000 points
Chain explosion of 3
Destroy four mechballs
Collect 175 coins in one game
Complete mission 3.3
Rescue B.A. Baracuda
Drive over 5 dudes with a tank
Complete mission 4.1
Drive over 10 dudes with a tank
Rescue Sarge
Score 2500 points
Complete mission 4.2
Blowup a death worm
Complete mission 4.3
Kill a flying fire skull
Complete mission 5.1
Kill 5 skulls in one mission
Complete mission 5.2
Destroy 5 hell tanks in one game
Complete mission 5.3
Complete Hell with Sarge
Complete Hell with BA
Rescue Sonya
Find the sketch world!
Kill a chicken, and spread some eggs!
Deactivate your first beacon
Take cover rookie!