Experiment No. Z-57 is a boss in Metroid Dread.
Experiment No. Z-57 is a large monster vaguely reminiscent of a lizard. It has six limbs; two extendable, spike-lined tentacles that serve as its main means of locomotion and physical combat, while the other four have distinctive joints and four hooked claws on their ends. The latter limbs can be folded against Z-57's body when unneeded. It seems to lack any hind limbs, save for a long tail which it may use for propulsion or support when moving. Most of its body is black or very dark-colored, save for its claws, spikes, and its twisted, skull-like head. Multiple yellow-orange eyes are scattered over its head, and its tripartite jaws are lined with jagged, tooth-like protrusions, Some cutscenes and animations show that it also has several long spikes dotted around its body, including what appears to be a partially exposed ribcage on its underside.
Experiment No. Z-57 has notable physical similarities to Corpius, with a very similar head and a similarly exposed ribcage, but their exact relation is unknown. Considering its name and the Chozo Archives, it is presumably one of the Mawkin tribe's artificial bioweapon experiments instead of a natural bioform.
An image in the Chozo Archives indicates that Quiet Robe had been directly involved in the experiments that created Experiment No. Z-57, most likely under Raven Beak's orders. Z-57 is first seen being experimented on in the background of a blacked-out room in Dairon; it can be seen in greater detail once Samus Aran turns the power back on. While the machinery operating on Z-57 still appears to be partially functional, the experiment remains unresponsive save for occasional twitching and does not react to Samus's presence.
Later in the game, after the X Parasites are released from Elun, Experiment No. Z-57's body vanishes from its room in Dairon. It is revealed to have been infected by an X before heading to Cataris, disabling the thermal generator in an effort to freeze the entirety of ZDR. Using her Gravity Suit to endure the sub-zero temperatures, Samus makes her way to the generator, finding it covered in strange slime that prevents its parts from moving. Moments later, Z-57 appears from above the generator and attacks her.
Upon its defeat, Experiment No. Z-57 collapses on the edge of the main platform, allowing Samus to force it off with several charged Arm Cannon shots. The monstrosity pulls itself up long enough to grab Samus in its claw, intent on dragging her with it; instead, Samus shoots it in the mouth once more, leaving it to plunge off the edge alone. Z-57 briefly reverts to its Core-X form before sinking in the lava below; Samus pulls herself up the ledge to see its slime disintegrate from the generator, allowing it to resume functioning.
Samus must shoot at Experiment No. Z-57's head to damage it, which is made more difficult by the boss being the only foe in the game who can briefly retreat into the background during certain moves. It attacks by sweeping the room with a beam of pink plasma; Samus must wait for it to pause in its sweep and jump to the other side of the room before it resumes firing, being careful not to touch the residue left in the beam's wake. It also swings its tentacles at Samus, requiring her to stay in the air near the opposite corner of the room from where the swipe is coming from.
After being shot in the head several times, Experiment Z-57 will slam a tentacle on one side of the room and fire a beam along the ceiling and the opposite wall, forcing Samus to move near its head to avoid damage. Should she dodge the laser, the creature will attempt a bite which can be Melee Countered to make Z-57 vulnerable; hitting it during this point will initiate a Grab Sequence that gives Samus an opportunity to deal significant damage.
As its health dwindles, Experiment Z-57 will use new attacks. It can grab the walls and ceiling with its auxiliary limbs, bracing itself for a targeted energy blast while slowly restoring its health; Samus can interrupt it by shooting the limbs (preferably with the Storm Missile), destroying them permanently and preventing it from using the attack for the rest of the battle. It can also perform a double swipe with both of its tentacles, forcing Samus to jump in the center of the arena to avoid damage. Its most elaborate attack fires its beam at the right wall, activating powerful fans that blow waves of crescent-shaped projectiles at Samus; she must jump through gaps in the waves to avoid being pushed into the damaging residue that appears on the left wall. Z-57 is left winded after this attack, allowing Samus to get some free shots in before the fans die down; alternatively, she can prepare a Shinespark, which can instantly defeat the creature if she can hit its head.
Experiment Z-57's Grab Sequence has Samus scaling its tentacle to jump on its head, firing all the while. The monster retreats to the thermal generator in an effort to shake Samus off of it, but she holds on and resumes firing as it rampages around the generator. After making a full loop of the device, Z-57 throws Samus off of its head; she uses her thrusters to land safely back in the battlefield as the boss leaps back to re-engage her if it has health remaining.
- Experiment No. Z-57 was first seen at the end of the Overview Trailer, and was seen again in greater detail in the third Japanese commercial.
- Raven Beak X exhibits features from Experiment No. Z-57, although they're much less prominent than Kraid's features; its head splits open similarly to Z-57's lower jaw, and it has a similar physique and method of locomotion (dragging itself forward on its long, gangly forelimbs, with no visible hind limbs). This implies that the Core-X that fell in the lava after Z-57's defeat somehow survived and was able to assimilate Kraid (who also happened to be defeated in the lava region of Cataris) before returning to Hanubia for Raven Beak.
- Experiment No. Z-57 is referred to as "Cooldown" in the game's files, referring to its role in causing the rapid cooling of ZDR.
- Part of the music used for this boss fight is a sample of Tension Before a Confrontation from Metroid Fusion.