Kill your first enemy.
Kill 10 enemies.
Kill 100 enemies.
Kill 1000 enemies.
Die by your own bullet.
Die 100 times in the campaign.
Unlock every character in the game.
Complete a Deathmatch against 1 or more friends.
Complete a 100 round Deathmatch against 1 or more friends.
Kill one of your teammates with a bullet while in the campaign.
Complete the campaign on Easy mode.
Complete the campaign on Hard mode.
Complete the campaign on Master mode.
Die while over half way through the campaign on Master mode.