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Bosses

(Mini-Boss of Brinstar)
Rock Worm  This worm attacks by smashing Samus with the claws on its face and rattling its sides. Its eye is its weak point.

Acid Worm This worm attacks with its razor sharp teeth. In order to defeat it, you must get it stuck in the rocks when it comes to attack Samus. Then blast it with missiles.

Kraid This giant lizard attacks with its claws and the spikes on its back. In order to defeat it, you must shoot its eye with a missile and when it opens its mouth blast his mouth with missiles.

Imago Larva This form of Imago can only be defeated by hitting its weak point under its belly. The second one Samus encounters must be defeated with the following steps: Plant a bomb and hit it with a missile.

Imago Cocoon This form of Imago can only be defeated by shooting the Winged Ripper with an ice blast and climbing on top it to shoot the tentacles attached to the Imago Coccoon.

Imago The final form of Imago. Its stinger is its weak point. The easiest way to defeat it is to climb to the top of the hill, duck, wait for it to appear, and run down the hill blasting its stinger with missiles.

Ridley This winged creature attacks with its tail and fireballs.

Mother Brain This creature's only attack is its laser but its weak point is its eye.

Chozo Ghost This creature mimics Samus's every move in the orb it holds. The only way to defeat it is to shoot the orb when it turns into an outline of a human. By doing this, Samus will regain her suit and weapons.

Mecha Ridley The last boss of the game. It attacks with its claw, missiles, and a laser. Its weak point is glowing.
 

Enemies

Bio Barrier This creature blocks Samus's  path, neither damaging or attacking her.

Bio Door This creature shoots out balls of plasma when Samus is nearby.

Bombu This creature shoots out lightning.

Bug These creatures swarm Samus and slow her down. They do not damage Samus, though.

Camera Do not get caught in the yellow light! It will set of an alarm.

Draken These ancient Dragons live in the lava and stick their heads out to blow fire at Samus.

Gamet Their bodies are covered by a super-hard shell.  They fly out of the airholes and attack Samus.  The red ones have twice the strength as the others.

Geega They come out through airholes and fly sideways.

Geruta The skin on these powerful opponents can generate fire and radiate the energy inside their bodies. The green ones are stronger than the red ones.

Holtz These creatures fly down from the ceiling, attack Samus and then fly back up.  Armor-plated like the Geruta, they are also armed with two horns.

Melia These move in groups and can pass through walls and rocks.

Mellow These creatures can pass through walls.  They like to chase after you in groups.

Mellow Hive The source of the Mellows.

Metroid This protoplasm in suspended animation was discovered on the planet SR388.  It clings onto Samus's body and sucks her energy.

Multiviola These simple-structure organisms are reflected off the walls and bounce around.  They are pretty powerful but are difficult to attack with the normal beam as the walls reflect them and they are always moving.

Nova Their entire bodies are covered in spiky, fireproof wool and they crawl around the floor.

Polyp These are poisonous lumps of lava that are blown out of the airholes.  They are weak enemies and can be destroyed with missiles.

Pounder The smaller cousin of the Dessgeega. 

Rinka These fireball creatures suddenly appear in the last scene.  Lots of them appear but they are not very strong.

Ripper These strange creatures do not have brains.  They simply fly around sluggishly in straight lines.

Ripper II The faster and much stronger Ripper.

Skree They stick to the ceiling and lie in wait for Samus.  When he approaches they spin downwards to attack him. The blue ones are the strongest.

Skultera Skeleton fish that is very tough to kill.

Space Pirate Alien troops that shoot plasma beams.

Squeept They emerge from the lava and sink back into it.

Stomper A much stronger version of the Dessgeega and the Sidehopper.

Tangle Weed Effective against smaller creatures, but does little damage to larger creatures.

Ultra Pirate A Space Pirate trained in martial arts.

Venom Weed A stronger version of the Tangle Weed. It uses its deadly toxin to subdue its prey.

Viola These are Multiviola larvae and they crawl along the ground. The blue ones are the weakest.

Waver  These powerful enemies flutter around in irregular patterns.

Winged Ripper This type of Ripper uses its wings to fly in circles.

Zebbo These bugs fly out of the airholes.

Zebetite This energy source is vital for keeping Mother Brain alive.  It is no more than a life-supporting system and therefore won't attack, but it must be destroyed and only missiles will do the job.

Zeela These boneless animals creep along horizontal and vertical surfaces.  They normally live underground.

Zoomer These fierce little creatures spray sticky fluid from their feet so they can move along the floor or up and down walls. The blue/yellow ones are the strongest.