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.
Complete all Achievements
Unlock all Illustrations
Save 1,000 POWs
Kill 1,000 soldiers
Play 100 times as Fio
Play 100 times as Tarma
Play 100 times as Eri
Play 100 times as Marco
Clear any mission with no miss
Save 100 POWs
Reach a score of 1 000 000 points with a friend
Obtain items from Madoka Aikawa
Get all weapons
Turn into a snowman
Clear the game without using a continue
Play with all characters
Kill 500 soldiers
Clear the game
Throw 300 grenades
Save 10 POWs
Save Hyakutaro Ichimonji
Reach a score of 500,000 points
Reach a score of 200,000 points
Reach a score of 100,000 points
Kill 100 soldiers
Clear Mission 1
Throw 50 grenades
Save an orangutan
Obtain items from Rumi Aikawa
Play with a friend