Here is the full list of all 30 Metal Slug 3 achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Unlock all Illustrations
Complete all Achievements
Clear the game without using a continue
Save 1,000 POWs
Kill 1,000 soldiers
Reach a score of 1 000 000 points with a friend
Play with a friend
Play 100 times as Fio
Play 100 times as Marco
Play 100 times as Tarma
Play 100 times as Eri
Save Hyakutaro Ichimonji
Kill 500 soldiers
Play with all characters
Save 100 POWs
Obtain items from Madoka Aikawa
Turn into a snowman
Throw 300 grenades
Clear the game
Get all weapons
Kill 100 soldiers
Reach a score of 500,000 points
Save an orangutan
Clear any mission with no miss
Reach a score of 200,000 points
Reach a score of 100,000 points
Clear Mission 1
Throw 50 grenades
Save 10 POWs
Obtain items from Rumi Aikawa