Metroid (NES) - Guide 

 Maru Mari (Morph Ball)

The Maru Mari is the first upgrade you can find, and you can't get very far without it. To reach the Maru Mari, go to the left immediately from the start and jump over the obstacles in your way; there are a few enemies to get past as well. You will quickly find the Maru Mari on a raised pedestal, walk into the item to collect it. The Maru Mari will allow Samus to enter narrow passages that are one tile high, and is good for avoiding enemies.

 

Missiles

the next upgrade to get should be the missiles, but missile upgrades are 

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