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