Colonel template icon.png
"Given your unofficial status..."

This article's title is conjectural.
Any name given in official media is eligible to become the title of the article.
The current title is not an official name.

For its room in Metroid II: Return of Samus and Metroid: Samus Returns, see Arachnus' room.

The "Arachnus' chamber" is a room on the Main Deck. It appears in Metroid Fusion.


At the start of Samus's mission on the BSL Station, her ship's computer directs her to this room after detecting bio-signs. This room is shown to have suffered significant damage, with debris being visible in the background. Additionally, the walls have a red hue, perhaps coming from an emergency light. In the background are large windows or blast doors, which appear to have a spin lock in their center.

Upon entering the room, the door locks behind Samus and an eerie theme begins to play. In immediate view are two ledges that Samus can use to climb over a wall, and then to climb atop another one. An Energy Tank can be found here, and just before a drop, Samus can fire a Missile at the ceiling to find a path to a second Energy Tank. On a 0% run, Samus must carefully jump over the Energy Tank to avoid collecting it.

After dropping down, Samus falls through four Pit Blocks into a small chamber below. A Core-X forms into a mimic of an Arachnus, a creature she previously fought during her mission on SR388.

While engaging the Arachnus creature, Samus can grab onto two higher ledges on either wall to avoid its incoming attacks. After defeating Arachnus, Samus absorbs its Core-X and regains her lost Morph Ball ability. From there, she can roll underneath the left wall and continue past more debris, into a ventilation shaft.

Because of the Pit Blocks, Samus cannot return to retrieve either of the Energy Tanks, if she did not collect them before, until she has obtained the Screw Attack. There are destructible blocks directly below the door that the Screw Attack can destroy.

Connecting rooms[]

The Core-X after its shell has been destroyed.



Morph Ball
Recovered after absorbing the statue's Core-X.
Energy Tank
In plain sight on one of the higher platforms.

Official data[]

Metroid Fusion: The Official Nintendo Player's Guide[]

6. BOSS BATTLE (pg. 21)

"After you drop into the area where bio-signs have been detected, you'll see a Core-X transform into an alien creature with a large shell on its back. Face off with the creature and hit it with Beam blasts or Missiles, then either jump over it or jump up to grab the nearest ledge. The creature's shots will fly under your feet. If you're hanging from the ledge, wait for the creature to roll up into a ball and charge the wall. Before the impact, jump away from the ledge and over the beast. The creature will turn to face you. Hit it with another weapon barrage and repeat the process. When the beast turns back into the Core-X, hit it with Missiles. Your reward for victory will be the Morph Ball data."
"One way to avoid damage from the shelled beast is to jump over it as it rolls toward you."
"After you switch places with the creature, hit it with several Beams or Missiles."
Tank Trials - 3 (pg. 106)
"You'll need all of the energy you can get on your way to the first boss battle. As you climb from ledge to ledge in the area above the target, you'll discover an Energy Tank in the middle of the path."

Metroid Prime and Metroid Fusion: Prima's Official Strategy Guide[]

Page 90
"Use back-flips to work your way up and over the ledge, and pick up another Energy Tank. Drop all the way down to a large chamber where you face Arachnus, a nasty monster that fires lethal energy blasts at Samus. If the blasts don't get you, the trail of fire will.
Making matters worse, the monster morphs into a spinning ball and plows into Samus. You must leap over the ball and immediately fire missiles at the Arachnus' back when it resumes its original form. This is when it is most vulnerable to penetrating fire.
After you destroy Arachnus, a Core-X remains. This is a circular shell containing a cluster of X. Continue firing missiles until you penetrate the shell and release the X (the Core-X damages Samus with every contact, so be careful). Grab the X before they float away. When you finally prevail, Samus regains Morph Ball ability. By pressing the + Control Pad down twice, Samus turns into a ball, which is useful for avoiding enemy fire or squeezing into narrow openings."
Page 91
"Morph into a ball and roll through the tunnel to the next section. Climb over the rock formation, then leap up to the opening. Hang on to the edge and press the + Control Pad up once to morph into a ball. Roll all the way through the tunnel into the next room, then use your new Morph Ball ability to navigate the narrow openings."