Here is the full list of all 15 METAL SLUG 2 achievements.
Clear Mission 1
Clear Mission 2
Clear Mission 3
Clear Mission 4
Clear Mission 5
Clear game (Final Mission)
Collect all weapons
Play with all characters
Kill 200 soldiers
Kill 2000 soldiers
Throw 50 grenades
Throw 200 grenades
Save 50 POWs
Save 200 POWs
Finish game without using continue