As Marco, Eri, Tarma, or Fio, you must defeat the evil General Morden and his henchman. To do this, you must defeat various enemies that get in your way. Throughout the game, you can collect new weapons including the Heavy Machine Gun, Shot Gun, Rocket Launcher, Flame Shot, Laser Shot, Flame Bottles, and Armor Piercer. Also scattered throughout the game, you can ride in four different vehicles (aka: Slugs) such as the Metal Slug, Slug Flyer, Camel Slug, and SlugNoid. By using these vehicles, you can cause awesome destruction against Morden's evil army. Other items such as energy, extra ammunition, and food (eat too much and your player will gain weight) are also found throughout the game.