Missile Expansions are arguably the most important collectible in Metroid II. Each expansion increases your maximum missile capacity by 5. Given that missiles are essential for defeating Metroids and opening Missile Blocks, collecting as many as possible is highly recommended.
Locations: Missile Expansions are scattered throughout every area of SR388. They are often hidden behind destructible blocks (shoot every suspicious wall!), in small crevices accessible only by Morph Ball, or on high ledges requiring the Space Jump. Some are even found in plain sight but require a specific sequence of actions or abilities to reach. Always be on the lookout for shimmering blocks or unusual environmental features.