The Zeta Metroid is the sixth natural stage of a Metroid's life cycle. They appear as enemies in Metroid II: Return of Samus and its remake Metroid: Samus Returns. They also have a minor appearance in the Restricted Lab of Metroid Fusion.
The Zeta Metroid possesses a very different structure from all prior forms, as it now resembles a reptilian dinosaur. This stage is the beginning of the species' adult phase, and thus requires a lot of firepower to kill. However a weak point can be exploited by shooting the Zeta Metroid in the dorsal region which multiplies the damage it receives. The Omega Metroid is the next and final stage for all standard Metroids.
After an undetermined period of time, a Gamma Metroid's backside splits open and the Zeta Metroid sheds the body like a butterfly sprouting from its chrysalis. The organism now possesses two arms and two legs with claws on each end, allowing it to stand in a bipedal position with a tail on its rear similar to an arthropod. Three blue compound eyes are present on each side of the head which is now separated from the rest of the body by a short neck. It now has a leech-like mouth and can spit hazardous substances. The creature is smaller than a Gamma Metroid, giving it quite a bit of maneuverability as it flies in the air. The membrane which houses its nucleus is located on its torso.
The Zeta Metroid's design is changed considerably in the remake Metroid: Samus Returns. The creature is far more slender and massive in height, with its arms, legs, and tail being much longer in length than Metroid II's design. The Zeta is mostly seen in a quadruped stance and can no longer fly. The head has been given an additional pair of eyes, making for a total of eight compound eyes instead of the original's six; they are now of a red color as well. Finally, the head of the Zeta Metroid is greatly elongated, reaching all the way to the middle of its back when the creature is on all fours.
In Metroid II: Return of Samus, the Zeta Metroid perpetually floats in the air, occasionally making quick dives toward Samus and then coming to a halt in order to spit large globs of damaging fluid. It is during this sudden stop that Samus can easily shoot Missiles at the Metroid's front. If she is skilled enough to outmaneuver the Zeta Metroid and get behind it, she can shoot at its back which multiplies the damage of each Missile nearly twofold. When first encountering the Zeta Metroid, it is seen emerging from the back of a Gamma Metroid, with the husk unceremoniously dropping offscreen.
Metroid: Samus Returns has a drastically different battle sequence for Zeta Metroids. Instead of flying, they crawl along the ground as well as climb on the walls and ceiling. As they do so, they will attack with either a medium ranged flamethrower from their mouths, or shoot long ranged green spheres of burning plasma-like energy. Occasionally, a Zeta will charge up the latter projectile while on the ceiling and launch a barrage of six; these charged projectiles will continuously bounce off of the room's surfaces and will not dissipate even if they hit Samus. It is at this specific moment that Samus can use her Grapple Beam in a similar fashion to the Grapple Lasso, grabbing onto the Zeta Metroid's back and smashing it against the floor. The creatures can also lunge at her as a melee attack which she can parry with her Counter; the Zeta Metroid quickly recovers and attempts to pounce Samus, but she keeps the creature at bay while continuing to fire at its underbelly.
The Zeta in Samus Returns is also much more durable, and its backside is no longer a weakspot as the shell will cause missiles to harmlessly bounce off. However, it can now be damaged by the Ice Beam.
"Multiple mutations will cause a Metroid to continue to grow into an even larger and more powerful adversary."
Nintendo Power issue 31Edit
"The fire-breathing Zeta Metroids are equipped with armor on their lower bodies. You'll only hurt them from the side."
- Zeta Metroid (p. 22)
- "This is the fastest Metroid of the bunch, at least relative to its size. Zetas are lizard-like Metroids that spend a good portion of their time fighting from the walls and ceilings of their respective hiding rooms while they spit acid and fire at their prey. They’re among the most cowardly of the Metroid family when it comes to fighting style—or maybe they’re the craftiest, using their climbing and projectile-spitting abilities to their advantage. Either way, expect a fight with a Zeta to be on the short side compared to most other Metroid-type fights, but one that involves an awful lot of dodging and precision strikes."
- The Zeta Metroid have a resemblance to the titular Aliens from the film series of the same name, and is perhaps another reference to the franchise. This similarity is further highlighted in Metroid: Samus Returns with its redesign (in particular its elongated head and its ability to climb on any surface), as well as the Zeta Metroid's debut where it drools over Samus, lowers its tail before dropping down and slowly lifting its head; this is a clear homage to the first appearance of a full grown Xenomorph in the movie Alien.