Darkling

Darkling is a Luminoth term used to identify Ing-possessed creatures and mechanoids. It is also used to identify original bioforms that can only be seen on Dark Aether.

According to scans, the Ing race were initially unaware of their ability to invade another being's body. They first learned to possess organic creatures early on in the war against the Luminoth until finally learning how to do the same to robots near the conflict's final stages (prior to Samus' arrival to Aether). Darkling-possession is the Ing Horde's solution into gaining access to the Light dimension, in which its atmosphere is otherwise fatal to them. An Ing invades the opposite dimension by creating a small portal and emerges in a gaseous form to possess the nearest being within its range, be it synthetic or organic. Its victim, once under complete control of the Ing that possessed it, gains an altered physical appearance following an Ing's entry: one change that is seen in all possessions is an overall purple/darker shade of color. Other possible changes are the growths of thorns and spikes on the possessed's body, and the least common mutation is the addition of a red glowing sphere on the Darkling; this sphere is likely the same cluster of red particles seen in several pure Ing.

Darkling-possession is also possible with deceased bioforms, however it seems that the time usually required for complete parasitic fusion (a mere few seconds) is exponentially extended in this case and until it is reached, the "resurrected" Darkling will have slow movements and reflexes (similar to a typical zombie).

A being combining with an Ing tends to greatly increase the former's natural health and/or attacks, while making them highly vulnerable to light based weaponry. However, if a powerful Ing were to possess a weak being for whatever reason, the resulting Darkling could potentially be weaker than the pure form of Ing. A lone Ing possessing an incredibly powerful being is seemingly impossible, and instead takes an untold amount of Ing to successfully take over such a being: this was the case for the Quadraxis drone.

A Darkling's body allows the dark Ing within to survive in the light dimension, and the presence of said Ing preserves the light body from deteriorating inside the corrosive dark dimension. Some Ing bring their possessed victims to their homeworld and add to the Ing Horde's numbers. As a result, the Ing army is composed of a variety of beings, ranging from mechanoids, wildlife and others. Early on in the war for Aether's planetary energy, the Luminoth were among the first to be targeted for Darkling-possession, creating Dark Luminoths (most likely one of the first species of Darklings to exist). The only way to separate an Ing from its host without the Ing's consent is to kill the host, which subsequently kills the dark creature with it.

Darklings usually have Aether counterparts, such as the Dark Splinter and the Splinter. However, some of them do not have any: the Dark Phlogus, the Amorbis, Darkling Tentacles and Nightbarbs are such examples. These creatures could be considered as original Darklings, as they were seemingly born on Dark Aether without having any light counterpart possessed and/or brought over to the dark world (though how they were created this way is uncertain).

Samus Aran and specially armored Luminoth seem to be immune from any form of darkling-possession, the former having acquired the Energy Transfer Module early on in Metroid Prime 2: Echoes, which generates a constant light energy from within, thus making it impossible for her to become a Darkling. If the special armor of a Luminoth were to break and allow access to an Ing, the wearer would be prepared to end his/her own life before losing his/her will. There are uniquely powerful Luminoths, however, that possess incredible stamina and psychic durability capable of fending off Darkling-possessions without the use of the mentioned armor: A-Voq was one such Luminoth that pushed away numerous Ings attempting to possess him.

Destruction of Dark Aether
It is unknown if any Darklings survived on Light Aether when Dark Aether collapsed, though it is a possibility, and it is known that at least one Darkling was kept as a specimen by the Space Pirates on one of their homeworlds and dissected for research purposes.

If any number of Darklings remain on Aether after the Luminoth awakened from their life-preserving stasis, it is probable they are being disposed of by the latter, given their deep hatred for the Ing race.

Trivia

 * Dark Phlogus, Darkling Tentacles and Nightbarbs are odd cases, because the only creatures that could potentially be their natural forms are only seen on other planets; the Puddle Spore and Reaper Vines are found on Tallon IV, while Nightbarbs on Bryyo share the same name. If the mentioned Darklings are not original beings, then it is possible that the Chozo, Luminoth and Bryyonians, having all met each other at some point in the past, had exchanged a few wildlife from their respective planets, thus explaining how the Ing were able to possess these extraterrestrial bioforms. Another possibility is that the Darklings' natural counterparts had low populations on Aether when the Ing first experimented with possessing other lifeforms, and wound up rendering all normal variants on the planet extinct.
 * The corpses of Keybearer Luminoths found throughout Aether seem to be wearing smooth, glowing armor pieces not found on living Luminoths nor among normal Luminoth corpses; these Keybearers were possibly wearing the special armors designed to protect their wearers from Ing possession.
 * Ironically, despite being Dark-based creatures, they are still vulnerable to the dark elements. For example, if a Dark Pirate Trooper stumbles upon Dark Water, it gets incinerated. Another example would be that the Dark Missile Trooper is ultimately weak to the Entangler's effect.
 * The Dark Tallon Metroid that was kept as a specimen by Pirates, seen in Metroid Prime 3: Corruption, was originally meant to be an "artificial" Darkling. The designer of the room in which it appears in, Matt Manchester, also wrote scans that can be read in said room, though some did not make it in due to text size limitations. An unreleased scan reveals that Space Pirates were attempting to emulate the necessary conditions into creating Darklings without seemingly knowing that Ing are absolutely required to possess and inhabit them. All of these attempts were met with failure:"Metroids exposed to the Dark Aetherian atmosphere displayed significant changes to their physiology and behaviorial patterns. Exposure resulted in altered cutaneous pigmentation, solidified carapace with superficial dermal striation, emergence of multiple luminescent ocular organs, and two additional cuspidate teeth. Advanced physical durability was observed, as well as more instinctual and aggresive behavioral tendencies. Subsequently nocturnal, Dark Metroid developed a fatally acute sensitivity to solar light. All attempts to recreate this atmospheric transformation have met with utter failure. Test specimens yield a 100% mortality rate. Experiments rarely live more than a few hours after artificial transformation is achieved. Of these rare instances, specimens require complete artificial sustainment. No sentient behavior has been observed in any instances. Failure attributed to unknown variables." [1]