Here is the full list of all 63 Gunslugs achievements.
Complete mission 2.2
Complete mission 2.1
Score 1000 points
Kill 5 skulls in one mission
Locate the arcade !
Grab energy drink
Blow up 4 dudes at once
Score 2000 points
Collect 150 coins
Get your train ticket and ride.. or run
Drive over 10 dudes with a tank
Complete mission 1.3
Score 500 points
Kill 5 guys from cover
Air kill a dude
Blow up 2 dudes at once
Collect 100 coins
Change the tune using a jukebox
Make a chopper crash
Kill 10 guys in a mission
Complete mission 1.2
Grab a new weapon
Collect 75 coins
Complete bootcamp
Complete mission 1.1
Deactivate your first beacon
Take cover rookie!
Find the voodoo priest
Rescue Sly Rocko
Collect 125 coins in one game
Rescue Willis KiYay
Drive a tank
Find "a" princess
Kill 20 guys
Take a jetpack ride
Kill 10 guys with grenades
Complete mission 2.3
Chain explosion of 2
Complete mission 3.1
Kill 50 guys in one mission
Complete mission 3.2
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
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
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!