Wave Beam

The Wave Beam, called such for its wavy pattern, and because it fires "wave energy" (Metroid: Zero Mission Instruction Booklet, p. 25), is a beam that Samus acquires in all of her games, save for Metroid Prime: Hunters, Metroid Prime 2: Echoes, and Metroid Prime 3: Corruption (though she gains the Annihilator Beam in Echoes, the Volt Driver in Hunters, and the Grapple Voltage in Corruption, which have a few similar properties). It fires wave energy (often in the shape of a sine curve) that can usually go through walls.

In Metroid and Metroid II: Return of Samus, the Wave Beam generated a single bolt that moved forward in a sine curve and passed through walls. It was stronger than the other beams. It also acted as such in Super Metroid, as long as the other beams had been turned off, with the exception of the Power Beam, which could not be turned off.

In Metroid: Zero Mission and Metroid Fusion the Wave Beam was a beam that could go through walls. In these games, it acted as a power-up to the normal beam(s) that Samus had acquired thus far. In Super Metroid, it could be added to any other combination of beams to make them go through walls and give them a waving trajectory, or be used alone, making a purple waving ball. In Metroid Fusion, it adds a "go through walls" effect to the already-acquired Charge, Wide, and Plasma Beams. In Zero Mission, it added a widening effect and a phase effect to whatever beams Samus has by that point (Samus could actually obtain the item without any other beams, but she could have the Ice, Charge, Long, and even Plasma beams by then, due to the game's non-linear nature).

In Metroid Prime, the Wave Beam takes on a different role. Here, it is one of the three "elemental" beams, it representing the element of Electricity. It is the first beam Samus achieves on her mission to Tallon IV. The Wave Beam does not go through walls. However, if the player is locked on to an enemy, the beam has a homing feature that can follow an enemy around until it hits. The Wave Beam is acquired after defeating a Sheegoth in the Chapel of the Elders, located in Phendrana Drifts. When fired normally, it launches three separate rounds that undulate inwards and outwards continuously with impressive homing capabilities. When charged, it fires a slower-moving single round that, when used on a few certain enemies, can cause a stunning effect. Its uses outside of battle include energizing Power conduits and opening Purple Doors. It is the only weapon that can destroy the Pulse Bombu and the Scatter Bombu. On a related note, if the Wave Beam is used on an Auto Defense Turret or a Mega Turret, it reacts in a similar manner to a glitch in real-life automated turrets.

Also in Metroid Prime, the Wave Beam can also be upgraded with a Charge Combo called the Wavebuster. This allows Samus to fire a perpetual wave of electrical energy at an enemy, and like the normal beam it has a limited homing feature which doesn't require a lock-on, but its range is somewhat low. This attack uses up ten Missiles to activate and uses five Missiles per second when holding the fire button. Although it has an extreme ammunition cost with less damage-per-missile than the Super Missile, it deals damage at an incredible rate, making it valuable at quickly defeating enemies in a pinch.

In Metroid Fusion, this upgrade was possessed by the haywire robot B.O.X. This is the second to last beam achieved by Samus on BSL, before the Ice Beam.

Trivia

 * In Metroid Prime, the Wavebuster combo is especially useful for destroying a Sentry Drone in the Phazon Mines equipped with invisibility as Samus is unable to lock-on to invisible enemies and getting a direct hit can be difficult otherwise.
 * The Wave Beam Arm Cannon formation looks exactly like the Light Beam from Metroid Prime 2: Echoes, and the Nova Beam from Metroid Prime 3: Corruption.
 * In Super Metroid, the Wave Beam shares a similar sprite to the Energy Capsules.
 * In the New Play Control! and Metroid Prime Trilogyversions of Metroid Prime, sparks of electricity no longer appear on the Arm Cannon when charging. Theories suggest this may be due to the way this and other visual effects were programmed into the original game, making it impossible to reproduce the effects on the Wii alongside the new aiming system.