Here is the full list of all 42 Gunscape achievements.
Finish the Blowfish campaign
Kill a dinosaur boss
Use the Freezethrower to slide 3 blocks
Kill a robot boss
Kill 100 AI enemies
Rate another player's map as good
Finish the first Blowfish campaign map
Create your first map
Publish your first map
Play your first Free-For-All DeathMatch game
Play your first Team DeathMatch game
Play your first Team Capture-The-Flag game
Play your first Gun Game game
Play your first Infection game
Play your first split-screen game
Place your first block in Build mode
Place 100 blocks in Build mode
Place 10,000 blocks in Build mode
Place a Checkpoint in your map
Place a flag in your map
Rate another player's map as bad
Build a multi-map campaign map
Kill an enemy player
Kill 1,000 players
Kill 50 players with the Speargun tripwire
Kill 500 players with the Gauss Rifle
Kill 1,000 players with the PFG
Kill 50 players with your Fists
Kill 500 players with the Dual Zhotguns
Kill 5 players with a knife
Kill 100 players with the ID Disc
Kill 100 players with the Flamethrower
Kill 1000 players with the E-Bow
Win 50 Deathmatch games
Win 25 CTF games
Win 25 Infection games
Won 25 Survival games
Program 5 Terminals
Steal 25 flags in CTF
Return 25 flags in CTF
Killed yourself 50 times
Kill 5,000 AI enemies