There are 25 distinct species of basic creatures that Samus will encounter throughout her mission to defeat Mother Brain. Zebes has a very harsh ecosystem, one that only the fittest can survive in, and these evolution of these creatures reflect that. In a world where resources are limited, only the most aggressive species have manage to survive such an unrelenting environment. Many of the creatures follow similar behaviors to one another, having evolved from a common ancestor at some point, and then branching out to different regions of Zebes and adapting to the local environs. Creatures with common traits are grouped together.
Zoomers and Novas
All crawlers continue to walk along the edge of whatever terrain they happen to occupy. They are easy to defeat from away, but they have a nasty habit of attacking Samus' feet where she can't fire. Use bombs instead. Zoomers are fierce little creatures spray sticky fluid from their feet so they can move along the floor or up and down walls. They are the first enemy that Samus meets. There are two kinds: Red Zoomers and less powerful Yellow Zoomers. The entire bodies of the Novas are covered in spiky, fireproof wool. It enjoys hot environments and can withstand tremendous heat. A missile blast will kill them. If using the normal Beam, it takes two blasts to kill the blue ones and four blasts to kill the yellow ones.
Zeelas and Violas
The crawlers that have taken up residence in the two bosses' hideouts are no more dangerous than their Brinstar and Norfair brethren. Zeelas are boneless animals that creep along horizontal and vertical surfaces. They normally live underground and the blue ones are the strongest. The Viola are Multiviola larvae and they crawl along the ground until they can float. It takes two blasts of the normal Beam to destroy the blue ones and four blasts or one missile to destroy the yellow ones.
Zeb and Gamets
Each of the flyers seem to take up residence in underground dwellings with openings that are exposed on floor and various platforms, through which they rise out and attack to defend their hives. Zebs are among the weakest opponents on Zebes. It takes one blast of the normal Beam to destroy the yellow ones and two blasts to destroy the red ones. The bodies of Gamets are covered by a super-hard shell. They appear out of the pipes in Norfair to attack Samus. The red ones have twice the strength as the others.
Geegas and Zebbos
The hideout flyers behave just like the others. They will climb to whatever height Samus is at before launching forward. Samus can fool them by jumping. Geegas have horns with deadly poison, and charge at you after appearing from vents. There are two types and the brown ones have twice the strength. Zebbos are bulked-up Zebs who can take more abuse than their brothers in the higher portions of Zebes. A single blast will lay the blue ones flat, but it takes two blasts to destroy the yellow ones.
Mellows and Melias
Swarms are made up of tiny insects that are rather weak compared to the bulk of Zebes' natural life forms. They make up for their diminutive stature by congregating in great numbers and overwhelming a source of food whenever it gets close by. Both Mellows and Melias have an odd ability to pass through the cracks in the walls that make up Brinstar and Norfair, so they can get to you through any obstacle. A single blast from a regular beam will destroy them.
Memus are the Hideout I equivalent of Mellows and Melias. They gather together in swarms in an effort to attack Samus before she can reach Kraid. If you happen to have the Screw Attack, you can take out an entire group of them in a single jump.
Rios and Gerutas
Swoopers are like bats; they like the cling from the ceiling and drop down on unsuspecting victims. They are quite strong and can take a large number of hits before dying. Rios occupy some of the ceilings throughout Brinstar. Purple Rios are stronger than the green ones. The skin of the powerful Gerutas can generate fire and radiate that energy throughout their bodies. Be especially careful of the strong red ones. They are the toughest creatures that appear in Norfair.
While Hideout I does not possess any Swoopers, Hideout II is the home to the strongest variety of Swooper imaginable: the Holtz. These creatures are much faster compared to a Rio or Geruta. They fly down from the ceiling, attack Samus and then fly back up. Armor-plated like the Geruta, they are also armed with two horns. It takes several blasts of the normal Beam or a single missile blast to destroy them.
Sidehoppers and Dessgeega
Hoppers, as their name suggests, like to hop. They bound and leap to attack their prey with crushing weight. However, there is one peculiar aspect about Hoppers that scientists can't explain: some Hoppers can completely defy gravity and hop along the ceiling instead! What is known for sure is that they are deadly in any orientation. Sidehoppers possess incredible strength and are most easily dealt with missile attacks. Likewise, Dessgeegas are the second most powerful enemy in their region after Ridley himself. The Screw Attack can help make short work of them.
Floaters are an odd type of creature. They are unique for a number of reasons, not the least being that they are completely indestructible. No amount of beam or missile attacks can destroy them. They are also quite mindless, content to simply float back and forth and attack whatever happens to get in their way. While you can't do much about removing them, you can do one thing with them: freeze them. Once frozen, Rippers actually make quite good stepping stones towards reaching higher platforms. Of course, they do thaw out after a certain period of time, so be ready to react when they start moving again. Interestingly enough, the dark red variety of Floater can be destroyed with missiles, even though the yellow type cannot. The Ripper II variety is much faster than their original cousin.
Skrees are quite common throughout Brinstar and Hideout I. They stick to the ceiling and lie in wait for Samus. When she approaches, they dive bomb, spinning as they fall. They use their wings like drills to descend from the ceiling and attack Samus. Eventually, they break through the outer crust of Zebes and drill deeper into the ground. When the crust breaks, rocks are thrown in four directions around the Skree that can hurt Samus if she's too close.
These simple-structure organisms enjoy extremely warm environments where they can ride the thermal currents and bounce around. They are pretty powerful and are difficult to attack with the normal Beam as the walls reflect them and they are always moving. Use a Power-Up item to boost power first. One missile blast will also destroy them. You have to be extra careful of them as they move much faster. These are the products of the life force that Mother Brain breathes into the molten rock. They have the same attacking power as the Holtz and the Dessgeega from the same habitat. (Multiviolas are slower in Norfair)
Wavers user their wings to fly erratically through the air. These powerful enemies flutter around in wave-like patterns. It's difficult to aim a beam at the Waver. Shoot at them or run and jump to avoid them. Like Rippers, Wavers are especially easy to take advantage of with the Ice Beam. If you happen to need a platform when a Waver is around, wait for one to fly at just the right height and freeze them for a simple solution. These enemies tend to drop large energy orbs, making them an easy source for replenishment once the Screw Attack is obtained.
Squeepts have adapted to the burning environment of Norfair. They emerge from the lava suddenly to catch their prey and sink back into it. Once you know where they are, and how high they jump, they will never change. Learn their timing to avoid them. It takes more than one blast of the normal Beam to destroy them.
These are poisonous lumps of lava that are blown out of the air holes. They are weak enemies and have no life force. They are fired off with a regular timing. Study the eruptions and make your move.
This ancient species lives in the lava. They stick their heads out to blow fire at Samus. If Samus is hit by their fire blasts, her energy will be depleted. The source of their fire comes from a rare plant that only grows in Norfair at certain times of the year. When the plant becomes scarce, the dragons lose their ability to blow fire, but this does not happen very often.
These fire ring appear unexpectedly throughout Tourian as the byproduct of the massive amounts of energy consumed by the Mother Brain. They are her last stages of defense. Up to three of them can appear at one time on the screen, but they are not very strong. You can use the Ice Beam to freeze them, at least temporarily. Sometimes that's better than destroying them since it slows down their appearance.
This protoplasm in suspended animation was discovered on the planet SR388. Unfortunately for Samus, they happen to be very compatible with the energy given off by her Power Suit. They eagerly cling to it, draining it of the life support that she needs to survive. They can't be destroyed directly with the normal Beam. Two steps are required to defeat them. First, blast a Metroid with the Ice Beam, freezing it solid. Second, use five missiles to destroy it. Defeated Metroids leave behind super energy and missile refills that quickly replenish your stock.
This is the head of Mini-Boss hideout number one. He shoots missiles from his stomach, and uses a spinning horn on his back to attack. Be very careful of his fierce attacks. If Samus gets hit by him, her energy will be weakened a lot. Missile attacks are the best way to kill him, but brave players favor a more direct approach by bombing him at his feet. Still other players may jump in the toxic pools to his sides while hitting him with the wave beam. Be sure that you have a lot of energy if you are going to attempt this dangerous maneuver. You will increase your missile capacity by 75 if you beat him.
Ridley is the head of Mini-Boss Hideout hideout number two. When you enter his chamber, Ridley begins firing balls of flame. He jumps up into the air and attacks Samus by spewing fireballs. His race is an original life form of the planet Zebes and Ridley is working for the Mother Brain. Three methods of attack can be successful. You can attack with missiles, either up close or from the right door. However, if you have the Wave Beam, you have two other options. You can barricade yourself between the left door and the barrier in front of it. Or you can drop down into the lava, and fire upwards through his platform. Keep jumping to minimize the damage from the lava. If you have obtained the Screw Attack, you can use it to deal some big damage by jumping into him. Make sure your energy tanks and missiles are filled up. Destroy him and you win 75 extra missiles.
Mother Brain lies in the central base of the fortress planet Zebes, the home of the space pirates. As the controlling force of the Metroid and the despoiler of the planet, Mother Brain is one of the most dangerous beings in the galaxy. is Samus' ultimate target. Its aim is to cultivate the Metroid to multiply and conquer space. Zeebetite is its energy source. You have to discover Mother Brain's weak point before you can launch a missile attack. In order to destroy it, 33 continuous missile shots are required. Her destruction will trigger a self destruct sequence, and Samus will have a limited amount of time to escape.