Baby Metroid

Walkthrough: After defeating Queen Metroid, another Baby Metroid will approach Samus. However, instead of killing this Metroid that thinks Samus is its mother, Samus decides to preserve its life. After the cutscene ends, head to the left and defeat any leftover enemies with Baby Metroid by your side. This little guy will also help destroy any pesky blue crystals you come across. As you collect a number of collectibles and Expansions, use the elevator you come to to get back to the Surface Area. Continue to defeat the enemies that stand in your way as you try to reach the outside.

Once outside, head straight to the Save Station and save your game. Whatever you do, DO NOT PROCEED FURTHER JUST YET. Instead, start backtracking through all the previous areas and collect the remaining collectibles to earn 100% Completion of each area. After you do this, and only after you do this, return to the Surface Area and reach your gunship, where the next cutscene will begin.

Missile Expansion #1: Use your Lightning Armor to make it through the flora in the same room you battled Queen Metroid in order to find this Expansion.

Missile Expansion #2: Once outside, there will be an Expansion above you that is surrounded by several crystals. Freeze one of the flying enemies in order to use them as a platform, getting close enough for Baby Metroid to break the crystals. Grab the Expansion after it does.

Super Missile Expansion #1: Use you Phase Drift to run across the breakable floor just outside the room you fought Queen Metroid in to find this Expansion.

Super Missile Expansion #2: After you use the Elevator to get back outside after defeating Queen Metroid, activate your Lightning Armor and use your Spider Ball up the left wall to find this Expansion.