The Charge Beam Beast, also known as Diorumu (ディオルム Diorumu ), Beam Beast, and X-56V, is the first boss Samus Aran may face in Metroid: Zero Mission (and thus, the entire timeline) on planet Zebes.
Once Samus obtains her first Missiles in Corridor No. 5 and heads back to the door, she will encounter this creature. It will entrap Samus by using its elongated body to block all exits and force her to fight it. The Charge Beam Beast attacks by rushing its head towards its target, damaging her with its horns and spikes. The worm's second method of attack is to shake the segment of its body that is closest to Samus; several thorns which cover its body will start falling off and rain down on her.
All Samus has to do is fire a Missile at the creature's eye when it opens its eyelid. Once Samus defeats it with three Missiles, she will obtain the Charge Beam. However, if the battle goes on for too long after Samus lands her first Missile, then the Charge Beam Beast will grow tired of fighting and leave.
If Samus does not kill the Charge Beam Beast in the first encounter in Corridor No. 5, she will also encounter it at Corridor No. 4 as she explores Brinstar. It will alternate between the two corridors until it is killed. Because this boss can be skipped, it is possible that the Charge Beam Beast will not be the first boss she defeats, and it is even possible to fight it after defeating Mother Brain. It can be killed with just one Super Missile.
The Charge Beam Beast ambushes Samus by emerging from the ground, and then it repeatedly lunges at her and rams her against a wall. During the fight, an Imago joins in and grabs Samus, holding her in the air while the Charge Beam Beast attacks with its pincers. When it tries to attack again, Samus has learned its attack pattern and fires at its head, blowing off its eye and one of its pincers. The defeated Charge Beam Beast collides with the Imago just after Samus breaks free of the latter's grasp.
- The Charge Beam Beast's battle theme is shared with the Acid Worm.
- It is neither revealed nor explained how and why the beast possessed the Charge Beam. It is possible that it unintentionally obtained the upgrade while digging through the tunnels of Brinstar.
- Despite the beast having the Charge Beam, it never uses the item's abilities, contrary to other beings Samus encounters in her later missions who use their respective Chozo items in some shape or form. A logical theory would be that the Charge Beam Beast has no beam weapon to begin with, thus making the Charge Beam item useless (one can easily imagine the Bomb item unusable without the Morph Ball). However, the boss' charge attack, in which it attempts to ram itself against Samus, can be a reference to the "charge" aspect of the item.
- The Rhedogian in Metroid: Other M bears similarities to the Charge Beam Beast in terms of fighting, such as their weakpoints in the form of their eyes. When Samus is unable to completely defeat them, they will retreat only to reappear in another area. However, it is possible to defeat the Charge Beam Beast any time it appears (depending on the player's skill), while the battles with Rhedogians and their outcome are determined entirely by the game's plot sequence.
- Although this fact is difficult to detect, the Charge Beam Beast keeps its eye open during its final dive into the floor while retreating from battle. It is thus possible to kill it in the process of retreating.
- It is also possible to get an extra hit on the Charge Beam Beast the instant the battle starts, as it opens its eye for a second, making it vulnerable to a Missile.
- ^ Metroid: Zero Mission: The Official Nintendo Player's Guide pg. 31
- ^ Metroid Zero Mission Official Site, romanized by Infinity's End from Metroid Database. Infinity's End has also suggested the moniker "King Worm" as a fanon name. See Talk:Charge Beam Beast#Name Romanization.
- ^ Metroid: Zero Mission: The Official Nintendo Player's Guide pg. 11
- ^  (dead link)
- ^ Metroid Zero Mission Official Site, as translated by Metroid Database