Diggernaut

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

Samus Aran first encounters it in a subterranean cave, and flees as it chases her. Much later on, she re-encounters the robot, and battles it.

Chase sequence
At some point in the game, Samus comes across the Diggernaut within the subterranean confines of SR388. Perceiving her as a threat, it prepares to attack. Samus attempts to shoot at it, but is unable to cause damage, and seemingly SenseMoves out of the way. The chasing 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. Several Moheeks and Wallfires are seen on the path, and serve as minor impediments to Samus. They also attempt to attack the drill, to no avail.

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 right before the Diggernaut's drill kills her. The Diggernaut, assuming her to be dead, retracts its arm and leaves behind the Space Jump.

Battle
Entering a facility, Samus is confronted by the Diggernaut once again, which 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 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 a rotating red laser beam. Samus can attack the faceplate with Missiles or Super Missiles while jumping over the beam. When the Diggernaut takes enough damage, it will fall down and plant its arms on the foreground. 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 several Bombs to damage a light purple core inside the drill. The attack will flow 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, releasing purple energy spheres to 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 body across the screen while sucking in air in an attempt to swallow Samus. Samus can roll across the floor and lay Bombs to cause minor damage to the faceplate, which gradually cracks as the battle rages on. 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 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 again, it will begin to use its vacuum attack again. 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. The Diggernaut will resume its previous attacks after some time. Samus can use her Phase Drift Aeion ability, which will slow down the Diggernaut in enough time for her to destroy all the weak points on the faceplate.

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, destroying it. It rewards her with the Power Bombs after it is defeated.

Trivia

 * The Diggernaut chase and battle theme was first heard in the E3 2017 trailer for Samus Returns, during the action portion.
 * 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 in 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.

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