Phazon Beam

The Phazon Beam is an immensely powerful beam weapon, that first debuted in Metroid Prime. Since then it has appeared in some form in the sequels, Metroid Prime 2: Echoes and Metroid Prime 3: Corruption.

In Metroid Prime
In Metroid Prime, the Phazon Beam is used against the final boss, the eponymous Metroid Prime. When the corrupted Phazon Suit comes into contact with liquid Phazon, it goes into "Hyper-mode", supercharging Samus' Arm Cannon and allowing her to shoot a continuous stream of destructive energy. The Phazon Beam is the only weapon that can damage the second form of the Metroid Prime. Unlike the Hyper Beam given by the PED Suit, which can be fired anytime as long as Samus has enough energy to spare, she must step into a small pool of pure concentrated Phazon to use the Phazon Beam, meaning it can only be used when Metroid Prime creates them. Samus can only utilize the Phazon Beam as long as there is Phazon to draw from; each shot uses up Phazon in the pool, so she must make the most of it. The Charge Beam is incompatible with this version of the Phazon Beam; holding down the fire button will allow for a continuous beam attack. This chaotic version of the Beam weapon is seemingly the precursor to the more controlled and streamlined Phazon Beam accessed through the PED Suit in Metroid Prime 3.

In Metroid Prime 2: Echoes
Samus also uses a sort of Phazon Beam in this game, although it is not an actual power-up. In the final boss fight, Dark Samus occasionally fires tiny balls of Phazon that Samus must catch with the Charge Beam. When three of these Phazon balls are absorbed, Samus can fire them back at Dark Samus to damage her dark rival; absorbing more than three does not increase the strength of the beam. Any beam will work with this, so charged Phazon versions of the Power, Dark, Light, and Annihilator Beams exist. This grants no particular benefit, though, but using the Dark, Light, or Annihilator beam will not waste ammunition while fused with Phazon energy. Strangely, when this shot is used outside of the fight (via hacking), it can open any door (with the exception of the Seeker Missile Doors, due to their unique opening mechanism), break any substance, and does extensive damage to bosses. It is sometimes referred to as the "Debug Beam", and is likely that it was used as a play testing tool, which grants it such functions.

In Metroid Prime 3: Corruption
Main article: Hyper Beam (Metroid Prime 3: Corruption) Once Samus attains the PED Suit, she gains the ability to enter Hyper Mode at will, using the Phazon implanted in her by Dark Samus to power it. This variant of the Phazon Beam is called the Hyper Beam. Unlike this weapon's predecessor, once she enters Hyper Mode, Samus can fire single blasts of Phazon energy or charge it up. The charged version of this has Samus shooting out a rapid-fire stream of Phazon energy, dealing significant damage to nearly any enemy and using 4 units of energy per shot. As the charged shot is firing, the tip of the Arm Cannon spins, and the whole action looks similar to a gatling gun firing.

Official Metroid Prime website
Weapon effect: Devastating effects on targets.

Weapon range: 3 - 10 m

Weapon potential: Lethal

"When Samus' Power Suit is corrupted by viral contamination, the Arm Cannon becomes capable of firing the powerful Phazon Beam. The Phazon Beam is only triggered in the presence of high concentrations of Phazon. The Phazon Beam has a devastating effect on its targets. The Charge Beam does not function when the Phazon Beam is active, but even the uncharged blast is fierce enough to make quick work of most foes."

Trivia

 * The Phazon Beam is the first beam in the Metroid series that required ammunition in order to fire. This occurred in the original Metroid Prime and required liquid Phazon in order to fire.
 * The Phazon Beam briefly appeared in the trailer for Marvel: Ultimate Alliance, where Samus jumped and then fired a powerful blast at the ground. This was the Phazon Beam. This, along with Samus and her other abilities, did not appear in the retail version of the game due to reasons of copyright with Nintendo.
 * If Samus stays in Hypermode right before a cutscene, the Hypermode aura around her will most often fade (this depends on the cutscene), yet the beam shape the Arm Cannon takes during Hypermode is retained.
 * The ending cutscene of Metroid Prime 3: Corruption has Samus with the Hyper Beam still on her Arm Cannon despite the fact that Phazon has been completely purged from her body.
 * In the Metroid Prime Trilogy, if Prime is selected for play from the main menu after obtaining the Phazon Suit, a loading cutscene will play showing Samus in her Phazon Suit, firing a move strikingly similar to the Zero Laser. Despite this, it can be seen that the Arm Cannon is in Phazon Beam configuration, showing that the Phazon veins which form on the Arm Cannon when using this beam also extend to her right shoulder pad.

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