Metal Slug Advance Hints & Cheats

Unlockables

"Complete" a mission
In a mission, rescue every prisoner and collect every available item (the X-Ray scan card is useful for this) to get a golden "COMPLETE" sign over a mission on the map screen.
Get the boss cards
When you are fighting a boss, you must destroy it very quickly to get its card (A message will appear on screen informing you that you have the card) To defeat the bosses quickly you must have lots of grenades and a special weapon (like the flame shot for the fourth boss) or use the Metal Slug if you can get it (Second, third and final boss)
Unlock the extra Dungeon mission
In Mission 5, find and collect the dungeon card. Then complete mission 5 and go to the mission select screen and to the top left there is an extra mission called dungeon.

How to Unlock	Unlockable
Kill 100 soldiers	Soldier A card
Kill 200 soldiers	Soldier B card
Kill 300 soldiers	Soldier C card
Kill 999 soldiers	Soldier D card
Don't kill any enemies and complete a level. Just die as soon as you start a level.	Washout

Unlock Decoration Card
You need the "paper thin" card. Turn it on, then complete any mission. With paper thin turned on you will die with just one hit. The easiest way to get the decoration card is to complete mission 2, mainly because there is a Metal Slug at the near start of the level which is shielded, so if you can manage to get through the level with the Metal Slug it shouldn't be as difficult to get the card.

You just have to clear the mission, you can die as many times as it takes.

Unlock All cards card
Collect all 99 cards in the game to get the final 100th "All cards" card.
Get Allen Jr's card
In mission 5, find and kill Allen. (He has a large machine gun, throws grenades and will slash you with a knife if you get close and is different to any normal enemy) When you do kill him, he will drop a card. Collect it, then complete the level without dieing to keep the Allen Jr card.

Parachute route in mission 5
In mission 5, jump into the plane slug. Now as soon as you start the level proper, press L to crash the slug. You will eject and go onto a different route where you parachute down into the enemy docks.

Bypass Airplane Level
After you jump into your plane slug in Mission 5 and go onto the next screen, quickly press up until you're on top of the screen, press left and hold it. Now the enemy planes won't show up on screen and if you hold your position long enough, you will finish the level without encountering any enemies.

Type	Name	File Size
Other	Card FAQ by Darkcyde	6K
FAQ/Walkthrough	FAQ/Walkthrough by Lemonhoax	96K
Other	Item Locations FAQ by CO Mel	18K
FAQ/Walkthrough	FAQ/Walkthrough by WK11239	40K

Hints & FAQs provided courtesy of GameFAQs.