Metroid: Zero Mission

Metroid: Zero Mission (メトロイドゼロミッション, Metoroido Zero Misshon) is a remake of Metroid, making it chronologically the first game in the Metroid series. It was designed to "retell the story of Samus Aran's original mission".

Zero Mission was developed by Nintendo's internal team, Nintendo Research & Development 1, under the direction of Yoshio Sakamoto. Zero Mission features a slightly different plot than Metroid, with new areas having been added.

Plot
In the year 20X5 of the Cosmic Calendar, the Space Pirates attacked a deep-space research vessel and seized capsules containing samples of an unknown species that had been discovered on planet SR388. The Space Pirates' objective was to acquire these life-forms: known simply as Metroids, these floating organisms were incredibly dangerous, as they could latch onto any other organism and drain its life-energy. Furthermore, it was possible to replicate Metroids in vast numbers by exposing them to beta rays. The hypotheses that the Metroids were responsible for one of the greatest mysteries in the entire galaxy — the extinction of all life on planet SR388 — was generally accepted as fact.

If the Space Pirates were able to breed the Metroids and use the creatures as biological weapons, the destruction of all galactic civilization would be inevitable. After a desperate search, the Federation Police discovered the Space Pirates' base of operations on the planet Zebes. They launched a full assault on the planet, though pirate resistance was strong, causing the Federation Police to retreat. Meanwhile, in a room hidden deep within the center of the pirate fortress, the preparations for multiplying the Metroids were steadily progressing.

As a last resort, the Federation Police decided to send a lone space hunter to penetrate the pirate base and destroy Mother Brain, the mechanical life-form that controlled the fortress and its defenses. Samus Aran was chosen for the mission, considered the greatest of all bounty hunters. Samus had successfully completed numerous missions that others had thought impossible before, making her an excellent candidate. However, despite her accomplishments, much of Samus's true identity remained wrapped in mystery.

"Planet Zebes...I called this place home once, in peaceful times, long before evil haunted the caverns below. Now, I shall finally tell the tale of my first battle here.... My so-called Zero Mission."

-Samus Aran

Samus Aran eventually landed on the surface of Zebes and began exploring the planet; the planet where she was raised as a child by the Chozo. Eventually, after making it through all the caverns and areas of the planet, Samus finds and destroys Mother Brain. However, upon leaving the planet, having successfully carried out her mission, Space Pirate Fighters attacked her gunship, causing her to crash back onto Zebes, crashing near the Space Pirate Mothership.

She explored the mothership and eventually reached the Ridley Robot, a mechanized form of Ridley. Upon defeating the Ridley Robot, Samus is able to successfully escape the planet by using one of the Space Pirate's shuttles. All the hard work the Space Pirates did, as well as the Metroids, were destroyed by a self-destruction.

General mechanics
As a remake of Metroid, Zero Mission's general layout is very similar to the original. However, new items, mini-bosses, and areas have been added, notably Crateria and the Space Pirate Mothership. Although Zero Mission can be a linear game, much of it can be completed non-linearly, making it possible to complete the game by collecting only 9% of all items. As with most Metroid games, you can save at save rooms and a map can be opened to navigate around the planet.

Zero Mission also differs from the original Metroid and the other Metroid games in that you can play as Samus without her Power Suit, making her more vulnerable to damage. This form is known as Zero Suit Samus. This marks the second time (the first was in the first Metroid game) she has been playable during the course of normal game play without her suit, whereas in each previous Metroid game, seeing Samus without her armor has been a feature in one or more of the game's endings or an easter egg.

Unlockables

 * If Normal mode is completed, then Hard mode is unlocked for the next play session. In Hard mode, damage taken is doubled, enemies are often added or replaced with tougher versions of themselves, and upgrades are less effective - with energy tanks only adding 50 energy to your total instead of 100, normal Missile Tanks adding 2 rather than 5 missiles to your supply, and Super Missile Tanks and Power Bomb Tanks adding just a single of each to your supply. Additionally, there are some minor map changes, most notably that certain save rooms have been removed.
 * If you clear Zero Mission on Hard mode, you unlock a music test feature.
 * If you beat the game on any mode, you unlock a pixel-perfect reproduction of the original Metroid.
 * If you connect Zero Mission to Metroid Fusion, you unlock a gallery showcasing many images of Samus from Metroid Fusion, images that were only available in the Japanese version of Fusion. Also, images of her past are displayed graphically telling her story from the raid of K-2L, her home planet, to her training with the Chozo.

Trivia

 * This game has a prequel manga depicting Samus' childhood, as well as some of Samus' history in the Federation and a small rendition of the game's events. It has been fan-translated into English.
 * Metroid: Zero Mission's code contains a left-out Crocomire sprite, which has ambient animations but is incapable of moving, attacking or taking damage. It is unfinished and has no death animations, indicating that it was going to be included but was later dropped. It is notable that this rendition of Crocomire does not have its signature rough skin, possibly indicating that the injury was intended to be inflicted in this game.
 * Two features have been found in the game's code. The first is the ability to toggle items on and off, much like Super Metroid (though the suits cannot be disabled, and the Bombs and Power Bombs can only be disabled when the Morph Ball is). The second is that Red Blast Shields take five Missiles to hit instead of the single Missile required in the final version of the game.
 * Metroid: Zero Mission is the first game that has part of the story take place while playing without the Power Suit.
 * There is a microgame based on the game in WarioWare D.I.Y.

Areas

 * Brinstar
 * Kraid
 * Norfair
 * Ridley
 * Tourian
 * Crateria
 * Chozodia
 * Space Pirate Mothership (only accessible after defeating Mother Brain. This area was not available in the original NES Metroid.)