Here is the full list of all 12 Ugly Americans: Apocalypsegeddon achievements worth 200 gamerscore.
Complete the game in an Xbox LIVE multiplayer session.
Complete the game using any character.
Complete all levels without using special attacks
Locate and collect all of the Demon Babies.
Collect all the projectiles.
Defeat 50 enemies in a row without getting hit.
Use any special attack 100 times.
Resuscitate 50 allies.
Rack up a 20 score multiplier.
Kill 1000 Manbirds.
Kill 300 Zombies.
Kill 5000 Demons.