Here is the full list of all 20 Guns, Gore and Cannoli 2 achievements.
Kill 75 enemies with headshots
Kill 150 Mafiosi
Kill 100 zombies
Kill 200 zombies
Kill 500 zombies
Kill 200 German soldiers
Destroy 15 vehicles
Eat 50 cannoli
Kill 5 ball-and-chain zombies in mid air
Kill 100 enemies with the chainsaw
Have 20 enemies killed by propelling airvents in the 'Secret Base' level
Defeat the U-boat
Defeat the Tank boss
Defeat the German Commander Boss
Defeat the end boss
Simultaneously kill 5 enemies with the rocket launcher
Consecutively kill 20 units with headshots
Survive the Raid using only the baseball bat
Finish the Thugtown level, using only the pistol
Kill a German soldier by dropping the churchbell on top of him in the 'Killing Fields' level