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