Morph Ball

One of the most prominent, integral, and representative items of the Metroid games, the Morph Ball, sometimes called the Morphing Ball, or the "Maru Mari," is the Alt-Form of Samus Aran that turns her into a sphere that is almost 1 meter in diameter. It allows her to explore small tunnels which usually lead to rooms with crucial items in them.

Morph Ball Mode is vital in defeating many bosses from the series, including Amorbis in Metroid Prime 2: Echoes and the Queen Metroid in Metroid II: Return of Samus. In non-Prime games, it usually plays an important role in escaping from enemies, such as in Metroid: Zero Mission. In almost every game, a combination of the Morph Ball and a Bomb is the only way to detach a feeding Metroid.

Exactly how it functions is unknown, but Prime concept art shows a large ball forming around Samus from her suit's material, then shrinking down to its miniature size, and in game, a core of energy is visible through the 'equator', indicating that Samus may transform into energy to fit in the smaller ball. On the other hand, Zero Mission design documents refer to the Chozo being capable of "unique transforming into a sphere," implying that the user's body is physically within the ball somehow.

Upgrades
The Morph Ball has many upgrades, such as the Bomb Module, Power Bomb, Spring Ball, Force Ball, Boost Ball, and Spider Ball. Metroid Prime 3: Corruption introduces the new Hyper Ball ability, which allows Samus to generate deadly arcing tendrils of Phazon energy around her when in Hyper Mode. In Metroid Prime Pinball, the Morph Ball is the ball the player plays with on the pinball machine and introduces the Force Ball.

In the three Zebes-based games, the player acquires it almost immediately after beginning the game.

Appearance
Throughout the series (most prominently in Echoes), the Morph Ball has changed in appearance according to suit upgrades. The Morph Ball when Samus is in possession of the basic Power Suit is a yellow, gold or orange hue and has three grooves which spiral outwards from the center on each side. Between the two halves is a ball of energy, which is believed to be the essence of Samus. The energy varies in color. With the Power Suit the energy is yellow, with the Varia Suit it is most often blue, although it is sometimes green or white. With other suits expansions the energy is often light blue.

In Metroid Prime, the Morph Ball changes after the acquisition of the Spider Ball. The energy inside becomes green and a spherical "dent" appears on the sides, and is filled by a green translucent hologram. It changes color scheme twice after this, to purple plating and a blue core when Samus gets the Gravity Suit, and to black plating and a deep orange coloured core when Samus is infused with the Phazon Suit.

In Metroid Prime 2: Echoes, after the Dark Suit is acquired, the Morph Ball becomes more wheel-like in appearance, in accordance to the shoulder pads of said armor. After the Light Suit is acquired, the Morph Ball becomes spherical again, but has a spiraling groove on the sides.

The change in the Morph Ball is less extreme in Metroid Prime 3: Corruption, as it has one change throughout the entire game (even after the Hazard Suit is acquired): a Phazon-blue ball with hexagonal tiles over it. Also in this game, if Samus touches a Liquid Phazon enemy while in Morph Ball mode, she will become engulfed by a portion of the creature, which will eat away at her suit.

Other appearances
According to a Space Pirate log in Prime, the Pirates found the Morph Ball to be a very curious and intriguing technology, but attempts at reverse-engineering the Morph Ball technology were abandoned after the first four test subjects of the Pirate prototypes were horribly crushed and maimed.

Dark Samus also possessed a twisted variant of the Morph Ball. She is shown using it in the second fight with her in the Sanctuary Fortress in Echoes, and creates Dark Echoes which can use the Morph Ball during the fight with AU 313 at the end of Corruption. On both occasions, she uses the Boost Ball and is able to generate massive amounts of kinetic energy at once, that propels her around the area at shocking speeds. Dark Samus's Morph Ball is similar to Samus's, and has an eye on each side in Echoes, and it may also in Corruption. It is very hard to actually make out the appearance of Dark Samus's Morph Ball in Corruption, because it is always traveling at great speeds. The energy surrounding it while it is using the Boost Ball also obscures its appearance.

Dark Samus' Morph Ball also heavily resembles the Glire, Glice and Glunder enemies in Super Smash Bros. Brawl.

Metroid (1986 manga)
"Maru Mari - Get this, and Samus' body will become round, allowing entry into narrow passages."

Official Nintendo Player's Guide
"As soon as you start, go to the left. Jump up and cross the high walls, then you can get hold of the Maru Mari. This is useful for going through walls or narrow passageways."

Super Metroid manual
"You can use the Morphing Ball to make Samus roll into a ball and squeeze into narrow areas."

Metroid Fusion manual
"Use this power to roll into a ball and move through narrow passageways. Press down twice on the Control Pad."

Official Metroid Prime website
"Weapon effect: N/A

Weapon range: N/A

Weapon potential: Medium"

"The Morph Ball is a modular upgrade to Samus Aran's Power Suit, allowing the bounty hunter to roll into a spherical shape. While in Morph Ball form, Samus can place Bombs, activate special switches and squeeze through tight spaces.

Like the Power Suit itself, the Morph Ball is upgradeable via several modifications located throughout Tallon IV."

Metroid Zero Mission manual
"This ability allows Samus' suit to curl into ball form and navigate narrow passageways. (Press down twice)"

Metroid Prime 2: Echoes
"The Morph Ball changes your suit into a compact, mobile sphere. Press X to enter Morph Ball mode. Press X again to leave Morph Ball mode.
 * Samus's Notes: Like the Varia Suit, the Morph Ball is modular. There are several modifications that can be added to improve performance."

Metroid Prime Hunters
"SAMUS has the ability to transform into a ball that can move at high speeds and access areas her bipedal form cannot. To enter the alt-form, tap the icon in the lower corner of the touch screen. Use the +Control Pad or A, B, X, and Y buttons to move the MORPH BALL. Use the touch screen for more precise control with gentle strokes in the desired direction. BOOST by quickly stroking in the desired direction or by pressing the BOOST button."

Brawl Sticker

 * Morph Ball Metroid Prime Pinball - [Weapon] Attack + 5  (Samus, Zero Suit Samus)

Trivia

 * In the original Metroid, the morph ball is called Maru-Mari, meaning "round ball."
 * In Metroid Prime, Space Pirate logs reveal that they had tried to copy Samus's Morph Ball. However, their prototypes predictably failed, with gruesome results.
 * The eyes in Dark Samus's Morph Ball may be the eyes on her hands, however her hand's eye is a darker blue.
 * The Morph Ball was slated to appear in Marvel: Ultimate Alliance along with Samus and several of her other abilities, however, they did not appear in the final game due to Nintendo not giving consent. The depiction in the trailer appears to be based on that of Prime as Samus charges forward several times, suggesting the Boost Ball was intended to appear as well.
 * The Morph Ball is featured in the Burger King toy Metroid Challenge, where the ball is controlled through a maze with a magnetic Wii Remote.