Diggernaut

The Diggernaut is a rogue Chozo mining robot and boss in Metroid: Samus Returns. It is a new boss, and did not exist in the original Metroid II: Return of Samus.

Samus Aran first encounters and awakens it in a subterranean cave, later encountering it near a broken Chozo Statue, fleeing as it chases her. Much later on, she re-encounters the robot and destroys it in a battle.

First encounter
While exploring Area 3 within the subterranean confines of SR388, Samus comes across a quiet room and encounters the Diggernaut buried in rocks. As only the eye is visible, Samus assumes it to be a red Grapple Point and pulls on it. The Diggernaut receives a surge of electricity and awakens, destroying the rubble that was blocking Samus' path. It stares at Samus for a moment before walking away.

Chase sequence
Later, as Samus is exploring the latter part of Area 4, a minor earthquake occurs and in the next room, she finds a broken Chozo Statue with its Item Sphere missing. Shortly after, she encounters the Diggernaut again. As a reaction to this, she charges her Spazer Beam and points it at the mining robot. Perceiving her as a threat, it prepares to attack using its right drilling arm. Samus attempts to shoot at the robot, but is unable to cause damage, and seemingly SenseMoves out of the way. The chase sequence then begins.

The Diggernaut chases Samus through a complex series of a tunnels with its drilling arm, while the robot itself can be seen in the background. Samus must evade the drill while overcoming obstacles such as grappling blocks, Bomb Blocks and Morph Ball chutes. If Samus comes into contact with the drill, she will be defeated instantly, unless she has a full Reserve Tank, in which case she can survive getting hit only once. Several Moheeks and Wallfires are on the path, and serve as minor impediments to Samus.

After some chasing, Samus drops down through a floor of Pit Blocks underneath the Diggernaut's drill, into a temporary safe zone. However, upon leaving this safe zone, the drill will immediately reappear. Samus will come across pools of water, which she must grapple over as she does not have the Gravity Suit at the time and thus the water will slow her down. There are more Moheeks in this area, which again may impede Samus. She will then come to a Grapple Point on the wall, which she must attach to to get through a short tunnel filled with spikes. Beyond this is another safe zone with an Ammo Recharge Station, and an exit through the floor, obstructed by Missile Blocks.

Dropping down again, the drill resumes its pursuit of Samus. The next set of tunnels include more pools of water, spikes, Grapple Points and poisonous vegetation, as well as more Wallfires. Samus will eventually come to a dead end, except for a small hole in the right wall. Samus jumps into this ledge and enters Morph Ball form, narrowly avoiding the Diggernaut's drill right before it can crush her. The Diggernaut, assuming her to be dead, retracts its arm and leaves behind an Item Sphere containing the Space Jump.

Battle
While exploring Area 6, Samus enters a room with another Chozo Statue in the path of an air vacuum. The Diggernaut is seen in the background, inhaling the statue and its Item Sphere. Later on, when Samus is confronted by the Diggernaut yet again, it chooses to battle her directly.

The Diggernaut attacks Samus from the background. The robot uses its rapidly drilling robot arms as its primary means of attack. It will bring the arms together and push them forward into the foreground, before pushing them against the walls in the room. Samus must use her Space Jump or Spider Ball to evade this attack. Next, it will thrust its arms forward, onto an invisible "fourth wall" and slide them from left to right across the room thrice, with one arm raised over the other. The upper arm will cascade up and down as it does so, with a brief opening allowing Samus to jump through. After this, its "faceplate" will come into the foreground and fire two rotating red laser beams. Samus attacks the faceplate with the Arm Cannon while avoiding the beams. When the Diggernaut takes enough damage, it will fall down and plant its arms on the foreground, but if Samus does not damage it fast enough, it will repeat its previous attack pattern. The sections of the drill will begin rotating to form a Spider Ball Track on the side. Samus must use it to climb inside the drilling arm, and lay a Bomb to damage a Bomb Slot-like core inside the drill. The attack will cause energy to surge into the Diggernaut itself and cause damage, while rendering the arm Samus damaged inert. Energy Capsules, Aeion Orbs and Missile Ammo will be released from the Diggernaut.

The Diggernaut will then slam its drilling arms into the ceiling, drilling it and releasing purple energy spheres that rain down on Samus while it targets her with its laser firing system. Samus can destroy the spheres for additional pickups, while avoiding the laser. The Diggernaut will then begin to sweep its head across the room while sucking in air in an attempt to crush Samus with its mouth. Samus can roll across the floor and lay Bombs to cause minor damage to the faceplate, which gradually cracks as the battle rages on. Using the Spider Ball will prevent Samus from getting sucked in. After taking enough damage, it will then begin to fire three rotating lasers, this time in a Y arc. Samus can attack the faceplate again in the same manner as before, and then destroy the core in the second drilling arm.

With both of its drilling arms damaged, the Diggernaut begins to use them as blunt weapons, slamming them onto the ground thrice. The impact also causes a shockwave that can damage Samus. It will then fire eight lasers from its eyes in two sets of four, with gaps in between for Samus to jump through. After slamming its arms into the ground a second time, it will begin to use its vacuum attack. After sustaining enough damage, the Diggernaut's faceplate will come into the foreground, lined with Spider Ball Tracks and featuring three weak points. Samus must attach herself to the faceplate and lay Bombs on each weak point, taking care to do so before the faceplate generates electric energy that will detach her, although the weak points can still be clinged to as they are not electrified. However, the weak points will be rotating clockwise and the bombs must match with a line on a second inner layer that is rotating counter-clockwise in order to deal damage. The Diggernaut will resume its previous attack pattern after some time unless Samus bombs all three weak points fast enough, similar to the previous parts of the battle when it can be damaged.

Once the weak points are all destroyed, the Diggernaut collapses and drops another Item Sphere. As Samus approaches the sphere, the Diggernaut begins to rise up one more time. Having run out of patience with the robot, Samus fires a charged Plasma Beam blast into the Diggernaut's eye without even turning to face it, finally rendering it unable to function. Once defeated, its body lies lifeless on the ground, with one of its drilling arms blocking the exit. Samus then shoots the Item Sphere and uses the rewarded Power Bomb to completely obliterate the Diggernaut, unblocking the path leading to Area 7.

2017 Nintendo World Championships
At the Nintendo World Championships on Oct. 7, 2017, Metroid: Samus Returns was the third game played as part of stage 1. The 24 contestants were challenged to complete the Diggernaut Encounter as quickly as possible. Players who completed the sequence in under six minutes would receive 12 points, and those who completed it in 3 minutes would receive 24 points. Players were not eliminated for dying and were allowed to continue until they either completed the chase or the time ran out. The players would receive their points when Samus reached the "hidey hole", or the small ledge she uses to escape the Diggernaut. Most of the losing contestants died repeatedly in the third phase of the sequence. Four contestants were shown as completing the sequence: Anthony V, Kyle W, Sunny K and Dan S. The championship game can be viewed here.

Metroid: Samus Returns Official Guide

 * Inhabitants & Eco System of SR388 (p. 23)
 * DIGGERNAUT
 * "The Diggernaut is an ancient Chozo machine created to dig out the caverns of SR388, giving the Chozo more space to build their settlement. The Diggernaut has since malfunctioned, or was set with some sort of security protocol. Whatever the truth is, the Diggernaut serves as a thorn in your side during most of your mission."

Nintendo of America tweet
"Diggernaut, a giant Chozo mining robot, adds new danger and tension throughout #Metroid: Samus Returns."

Trivia

 * It is possible that the Diggernaut wasn't originally hostile to Samus, as it didn't attack her in the first encounter, after Samus grappled it. This is even more likely the case as seen later in the second encounter, prior to the tunnel sequence; the Diggernaut appeared to be simply curious about Samus, until she pointed her charged beam at its eye, which provoked a reaction (subtly startled expression and eye glowing stronger), effectively perceiving Samus as a threat. It is also possible the Chozo programmed it with some security directives.
 * The Diggernaut chase and battle themes (the former is shorter than the latter) are remixes of the Arachnus-X theme from Metroid Fusion and are similar to the Berserker Lord's adaptation in Metroid Prime 3: Corruption. The latter was first heard in the E3 2017 trailer for Samus Returns, during the action portion.
 * The Diggernaut was first hinted at in the ending of the Overview Trailer, where the narrator mentions that not even Samus knows for sure what nightmares she will encounter in the depths of SR388. As he says this, footage is shown of Samus looking down a cliff and seeing a red orb and a silhouette.
 * The Diggernaut's Spider Ball Tracks and Bomb Slot-like cores on its digging arms may be a reference/homage to the ''Prime series.
 * Diggernaut is similar to Quadraxis in Metroid Prime 2: Echoes as both are rogue, robotic bosses that feature puzzle elements, Spider Ball Tracks and Bomb Slots.
 * The final portion of the battle with the Diggernaut, where Samus attaches herself to the boss using the Spider Ball in order to lay Bombs on weak points, is similar to the Chrysalis phase of the Emperor Ing battle, also from Metroid Prime 2: Echoes.
 * The name "Diggernaut" is a portmanteau of the words "digger", referring to the robot's original purpose for mining, and "juggernaut", which refers to its massive size and power.
 * The Diggernaut shares a similar role with the Rhedogian and B.O.X. Security Robot as an enemy that attacks Samus throughout her mission and later battles her as a boss.
 * According to Yoshio Sakamoto's comments prior to a presentation of Samus Returns at PAX West 2017, the Diggernaut was used by the Chozo to mine into the center of SR388 when they were building their colony there.
 * This can be inferred in-game as it appears in the background of the 3rd Chozo Memory, where the Chozo are busy building it, as well as the seventh.
 * Several other robots of a similar design can be seen in the background of Area 3; smaller ones are also shown fleeing through the massive doorway in the cutscene prior to the Diggernaut's boss battle.
 * Before the chase sequence, it is heavily implied that the Diggernaut destroyed the Chozo Statue and took its Item Sphere containing the Space Jump.
 * This is supported when it takes the Power Bomb from another Chozo Statue in Area 6. The reason behind this behavior is unknown.
 * Using a Power Bomb during the Diggernaut fight (obtained early through an out of bounds glitch ) will force the Diggernaut into its post-battle exploding animation and destroy the obstruction to the next room, although it will not drop the Power Bomb Expansion when killed this way. If the Spider Boost is used to exit the room before the Diggernaut fully explodes, it will still be alive when Samus enters its chamber again.

Notes and references
Diggernaut