Here is the full list of all 42 Combat Racers achievements.
Die in Deathmatch
Unlock the secret character
Kill an opposing racer in Elimination
Kill two opposing racers within a second in Elimination
Kill three opposing racers within a second in Elimination
Be the only player alive without killing anyone after a round of Elimination
Don't die once in a full game of Elimination
Kill a total of 1000 racers in Elimination
Kill an opposing racer within one second of respawning in Deathmatch
Kill five racers without dying once in a single round of Deathmatch
Kill ten racers without dying once in a single round of Deathmatch
Kill a total of 1000 racers in Deathmatch
Respawn 160 times in total
Win a game using only Flamethrowers and the Backburner
Win a game using only Rocket launchers and landmines
Win a game using only Shotguns and Oil
Win a game using only Lasers and Cluster bombs
Win a game using only Sniper rifles and Flaming oil
Win a game using only Grenade launchers and Cluster Bombs
Win a game using only Crossbows and Caltrops
Win a game using only Railguns and Oil
Win a game using only Tank Guns and the Landmine
Win a game using only the Machine gun and Flaming Oil
Kill 100 racers using the Tank Gun
Kill 100 racers using the Landmine
Kill 100 racers using the Caltrops
Kill 100 racers using the Crossbow
Kill 100 racers using the Machine Gun
Kill 100 racers using the Shotgun
Kill 100 racers using the Sniper Rifle
Kill 100 racers using the Grenade Launcher
Kill 200 racers using the Flamethrower, Backburner and Flaming oil
Kill 100 racers using the Rocket Launcher
Kill 100 racers using the Laser
Kill 100 racers using the Railgun
Kill 100 racers using the Autocannon
Score a total of 1000 points in Banner Carrier
Finish your first game of Combat Racers
Commit 100 suicides
Kill a total of 15,000 racers
Kill a total of 40,000 racers
Kill 100 racers using Cluster Bombs