Imago's larval form, the Kiru Giru, was found in Norfair. After traveling through a Norfair tunnel infested with parasitic Tangle Vines, Samus encountered a larva that had been suspended in midair by the Tangle Vines ensnaring it. She freed the larva by using a nearby Winged Ripper to reach a position where she could fire Missiles at the vines holding the larva up. Once freed, the larva plunged into a stone platform, opening a passage leading to Ridley's Lair. If the Ripper is directly underneath the larva when it falls, it is killed instantly.
Soon after arriving in Ridley's Lair, Samus saw the Kiru Giru larva forming a cocoon after having dug deeper underground. Samus returned to Norfair and followed the larva's tunnel only to find that it had already molted. Following its burrow further, Samus discovered a new chamber lined with eggs; as she approached a blocked-off Super Missile Tank, she accidentally broke several of the eggs. Enraged at the threat to its offspring, the fully-grown adult Imago promptly attacked Samus.
Imago attacks by flying around and attempting to impale Samus with its deadly stinger. It will also fire needles from the stinger, and they can be destroyed for power-ups if necessary. This can be easily avoided, though, as Imago flies at a height that allows Samus to simply duck or use the Morph Ball to pass under it. Once she deals enough damage to its large glowing abdomen, the Imago's stinger is destroyed, leaving it only able to to ram its opponent. At this point, if Samus approaches the wall that blocks off the Super Missile Tank, the mortally wounded Imago will crash through the wall and expire, giving Samus access to the power-up.
There is a method to avoid damage entirely when facing Imago. By positioning Samus barely at the bottom of the first slope upon entering the chamber (her feet should be even with the first 'indent' near the bottom of the slope) and crouching, Imago's stingers will hit just in front of her and sail over her head while Imago remains unable to ram Samus. Samus will remain able to shoot Imago's abdomen at least twice per pass.
In Chapter 15 of the Metroid manga, Samus is attacked by an Imago while fighting the Charge Beam Beast. Her dialogue implies that the Imago (along with the rest of the Zebesian ecosystem) has heightened aggression due to being controlled by Mother Brain.
The Imago and Charge Beam Beast fight Samus together, with Imago holding her in the air while the Beam Beast strikes with its pincers. After shooting the Charge Beam Beast in the eye, Samus breaks free of the Imago's grip and shoots it as she falls to the ground.
Yoshio Sakamoto: "They're the same life form. But I don't know if it has tenacity. Samus only coincidentally narrowly saved the Kiru Giru captured by the Karamutsuta from certain death, and afterward, the reason Kiru Giru that became an Imago attacked Samus was because Samus had trampled on the eggs it had created."
- Since they are the same species, Imago's theme is a sped-up remix of the themes for the Kiru Giru.
- If Samus attempts to kill the Imago using a Spin Jump Attack, a glitch will stop it from moving. This forces the player to reset the game.
- Imago is the scientific word for the adult stage of an insect, such as a butterfly.
- Imago is called Kiru Giru (キル · ギル) in Japanese (sharing its name with the larvae), while its English name originates from Metroid: Zero Mission: The Official Nintendo Player's Guide. However, Yoshio Sakamoto referred to the adult form as 成虫, which can be translated as imago.
- If Samus has acquired a Super Missile Tank through Sequence Breaking, she can open the Green Hatch and skip the Imago entirely. Additionally, Samus can make use of her regular Missiles and the Bomb Jump to enter the other side of Ridley's Lair, allowing her to battle Ridley without ever going anywhere near the Imago.