Metroidis one of the longest running Nintendo game franchises not named Mario or Zelda, being a groundbreaking video game series by starring a female character, Samus Aran, as well as gaining critical acclaim for its gameplay and strong science fiction setting. Anyone who has ever played any installment in the series can vouch for the inspiration it has taken from the Alien franchise, up to and including the horror elements in its designs. Most of the creatures Samus fought over the years can look unnerving, but a select few can be called truly horrific. WithSamus Returns, the remake of Metroid 2: The Return of Samus, coming for the Nintendo 3DS and a new Metroid Prime installment coming to the Nintendo Switch in the future, let's look back at ten of the most frightening enemies that the bounty hunter Samus Aran has ever faced over her long career.

10. Mother Brain

'Super Metroid' © Nintendo

The brain in a jar wouldn't be considered a scary image by today's standards, even with the added difficulty spike it brought in the original NES title Metroid. And to be fair, this final boss was not that frightening in the final stages of the SNES classic Super Metroid either...until it gained a new form after Samus seemingly kills it a second time.

Gaining a large robotic body, sharp talons, teeth and a single eye, Mother Brain went from being somewhat silly to absolutely horrifying after this transformation. After coming this far and beating so many enemies, it can be nerve wracking when the player first faces this terror, as none of the weapons in Samus's arsenal seem to affect it. Though the intervention by the baby Metroid Samus saved in Metroid 2: The Return of Samus allow her to gain second wind (and a new power beam), the feeling of dread that comes from being brought so close to death after coming so far is horrifying to any player.

While silly at first glance, Mother Brain's final form is an unnerving sight to behold. So much so, that the scene was revisited in a cutscene in the much maligned Metroid: Other M. Bringing back this grotesque example of body horror was one of the few true highlights of the controversial game, showing just how much the image of Mother Brain haunts players to this day.

9. Ridley

'Super Metroid' © Nintendo

One wouldn't think "space pirate dragon named after Ridley Scott" would be as terrifying to behold as this monster. And yet he is. With his signature battle theme playing each time Samus faces him and his bone chilling war cry when he attacks, Ridley is rightfully a mainstay of the Metroid series, gaining the de facto title of Samus' arch-nemesis.

But the true sense of terror that comes with Ridley is the personal element. What sets the leader of the dreaded space pirates aside from the other enemies that Samus has faced is his role in her origin story. As revealed in the Metroid manga (and alluded to in Metroid: Fusion and Metroid: Other M), Ridley was responsible for the massacre of the space colony K2-L, leading the pirate raid and personally murdering Samus' mother Virginia before her very eyes. The player can practically feel the dread and trauma during the small cutscene in Metroid: Zero Mission, when these painful memories are brought up again in the seconds before the battle with Ridley begins.

A classic character in the series, but bringing sheer terror with each encounter, it is no wonder that Nintendo has included him in each installment of the Super Smash Bros. series in some capacity, as he is one of the great scary Nintendo villains.

8. Draygon

'Super Metroid' © Nintendo

Claustrophobia is a common occurring fear. The feeling of being constrained, trapped and unable to breathe. Now imagine that sensation taking living form, grasping you in its talons and draining the life from you with a hooked tail, and you get Draygon.

Samus first came across this creepy green creature on board the wrecked ship in Super Metroid. There isn't much fanfare to it when she first enters its submerged domain, running into a school of smaller versions of it (which we are to assume is its brood?) that flee upon seeing Samus. Then, without any warning, the Draygon zooms down, shrieking a terrible sound (which was sampled from Toho's daikaiju Anguirus), trying to grasp onto Samus. The speed at which it dive-bombs the player can be unnerving, and the inevitable low-health alarm that follows once it drains Samus of health just adds to the tension. Funny enough, one of the best strategies when dealing with this hideous creature is to shoot Samus' grapple beam into live electricity, damaging both herself and the attacking monster, showcasing just how desperate the situation is for Samus to have her resort to such drastic measures.

Draygon has only appeared once in the series but is a true horror for anyone with a fear of tight spaces, insect-like arms and that icky green color of its skin. Any player will shudder at the sound of its shriek.

7. Nightmare

'Metroid: Fusion' © Nintendo

The name speaks for itself. In fact, it almost sounds like it is trying too hard to convince you of how frightening it really is. But Nightmare lives up to its name, especially in regards to how it changes upon being damaged.

First appearing in Metroid: Fusion and making a comeback in Metroid: Other M (making the latter game its first chronological appearance), Nightmare is a bizarre fusion of technology and biology, resembling living mucus placed into a mechanical body with elongated arms, giving it a ghostly appearance. Its grotesque shape combined with the ability to warp gravity and an eerie battle theme create a disorienting environment akin to being trapped in a haunted house.

The true horror of Nightmare comes with defeating the enemy. Each time Samus manages to hit the creature's weak spot, it slowly melts and becomes more gaunt, upping the tension as the enemy grows more horrific the closer it gets to death. The sight of its decaying visage will stick with the player long after it has been defeated, leaving Nightmare as one of the most memorable enemies in both games it appeared in.

6. The Ing

'Metroid Prime 2: Echoes' © Nintendo

When Metroid took a Lovecraftian turn by introducing the Ing in Metroid Prime 2: Echoes, it gave way for the true face of terror that one imagines when they think of the phrase "cosmic horror." Part eldritch nightmare, part "bug" from Heinlein's Starship Troopers, and utterly nightmarish, there is no wonder that Metroid Prime 2: Echoes has scattered these enemies throughout the game.

These creatures come from a parallel dimension known as the Dark Aether, entering the "light" world through a substance called the "black fog." Their adversaries, the peaceful Luminoth, dubbed them the Ing after their word for "terror," and it's not hard to see why. Appearing as three-legged spiders made of pure darkness, swarming over their enemies in vast numbers and even copying the abilities of their foes (in several cases, those of a certain bounty hunter), the Ing can be seen as the fear of the dark made manifest. What's worse is their ability to cling to a host and merge with them, basically creating a fusion of horrific space aliens and pure darkness.

The Ing came in many versatile forms, but their theme of utter blackness and terror can be found throughout their species. Their presence looms throughout the game, literally and figuratively, overshadowing all other enemies the game throws at Samus.

5. Aazelion

'Metroid Prime 3: Corruption' © Nintendo

What is more terrifying than the unknown? One of the more world-building and expansive features from the Metroid Prime series is the ability to scan and obtain information about the enemies that Samus faces. All the more shocking when, during the final stretch of Metroid Prime 3: Corruption's final stage, Samus is suddenly attacked by this demonic looking creature simply known as Aazelion.

On the world of Phaaze, which has been consumed by the toxic Phazon, this unknown beast latches onto her with its many teeth and multiple jaws and attempts to swallow her whole. After facing so many powerful enemies, only to be snared and brought close to death at the very last possible moment, this sudden adversary is the stuff of nightmares. The creature can be killed at great cost to Samus' health tanks, adding even more dread to the final showdown of the game. And the cherry on top this horror sundae? Once Samus scans the creature, there is no data to be found.

What is the Aazelion? Why is it there? What kind of an environment would it require it to hunt like it does? Many questions are asked and no answers are given. And perhaps the lack of these answers is the most terrifying thing of all.

4. Metroid

'Metroid: Other M' © Nintendo

Being the creatures from where the series takes its title, there are few creatures in these games that are as terrifying as the Metroid. Taking inspiration from the Alien franchise, these creatures hunt indiscriminately, latching onto life forms and absorbing their energy until there is nothing left but an empty husk. Their only weakness is sub-zero temperatures, which Samus exploited with the ice beam in the original Metroid for the NES and most subsequent games.

While terrifying enough in their first appearance, Metroid 2: The Return of Samus upped the ante by revealing that the jellyfish-like form is but stage one of their metamorphosis, which eventually gain more teeth, more eyes and large talons, leading to Samus' confrontation with the dreaded Metroid Queen. Later games went even further, such as the Phazon corrupted Metroid from the Metroid Prime series, which could have large tentacles or split themselves in two.

Samus eventually made her peace with the creatures after she grew to care for an infant Metroid that sacrificed its life to save her (told brilliantly with minimal dialogue in Super Metroid, and poorly with the opposite approach in Metroid: Other M), so we can be forgiven for thinking that Metroid look cute as infants. But behind that image remains the terror that could end life in the universe if ever let loose.

3. Chozo Ghosts

'Metroid Prime' © Nintendo

The Chozo are portrayed as a noble species, having adopted Samus as a child after the death of her parents and granting her the power suit which she dons into battle. They never physically appear in the games, but their benevolent presence can be felt throughout the franchise from the artifacts and relics they have left behind that help Samus on her quest. In the spin-off Metroid manga series, these bird-like aliens are shown to deeply care for Samus. Thus, all the more terrifying when her former guardians are reduced to corrupted disembodied spirits, lashing out at her from beyond the realm of the living.

These enemies from the first Metroid Prime game strike at random times, dimming the lights in the area that Samus is in and starting their own unnerving battle theme. Their erratic attack methods, combined with them shifting in and out of sight, makes battling these lost souls a nerve wracking experience for any player.

Throughout Samus' journey on Talon IV she finds bits of Chozo lore that tell the story of the collapse of their colony on this doomed planet. These slight glimpses into their demise and the sight of the ghosts that are left in their wake can be terrifying, especially considering how destructive the effects of the dreaded Phazon must be to turn such gentle creatures into these terrors from the afterlife.

2. Metroid Prime

'Metroid Prime,' 'Metroid Prime 2: Echoes' © Nintendo

What is worse than a Metroid, an energy sucking parasite? What about a mutant Metroid created by the toxic Phazon, a translucent creature encased in a nigh-indestructible armor.

Hidden beneath the impact crater on Talon IV, this dreaded creature lives off the Phazon that has been killing the planet, basically giving a face to the dangerous radiation that is lethal to the touch. Once Samus destroys its armored casing, its true form engages her in battle, using its ability to vanish from sight to launch surprise attacks on her. The Metroid Prime can not only fire beams of pure radiation but spawn more Metroid from its own body, using them to distract Samus as it launches further attacks. Samus is forced to fight this monstrosity in the darkest depths of the impact crater, disorienting her by vanishing from sight and forcing the hunter to switch between multiple visors and and convert the deadly Phazon into a short burst weapon against the corrupted Metroid.

After the tense high-stakes battle against the monster, Samus rested easy knowing she had annihilated the source of the dreaded Phazon...until it was revealed the Metroid Prime fused with Samus' power armor to create the equally deadly Dark Samus, who would return and antagonize her in further Prime titles.

1. SA-X

'Metroid: Fusion' © Nintendo

If the Metroid were inspired by the Xenomorphs from Alien, then the SA-X is made from the same cloth as The Terminator. Appearing in the GBA title Metroid: Fusion, the SA-X is one of the X virus copying the abilities of Samus herself. While the idea of an "evil" Samus would be revisited in the Prime series with Dark Samus, the SA-X is far more terrifying, taking the familiar form of Samus from the previous games and turning it against the player.

Whenever it appears, the music stops, replaced with the heavy steps of the copy marching back and forth in search of Samus. Its attacks can easily kill Samus, so fighting is not an option. Even when she obtains the ice missiles, the copy thaws quickly and continue the chase. The only way to survive against the SA-X is to run; run and hide and pray it does not find you. Only after Samus has collected all the upgrades does she stand a fighting chance...which causes the SA-X to mutate even further into a horrendous beast. Did we mention there are several throughout the game, quietly stalking Samus and striking at her when she least expects it. For once, the hunter had become the hunted.

Many other games (especially from Nintendo) have the player fight a dark mirror image of themselves, but none are as terrifying as this dead-eyed creature that single-handedly turned a science-fiction platformer into a horror film by its mere presence. Good luck with keeping the sound of its footsteps out of your nightmares.