Metroid Fusion Walkthrough - Route, Upgrades, SA-X, and 100% Planning

Metroid Fusion by Nintendo R&D1, published by Nintendo, is a mission-led 2D Metroid game. Instead of dropping you into a fully open map, it routes Samus through the B.S.L. station by Navigation Room objectives, Data Room downloads, Core-X boss rewards, and late-game cleanup.

This guide is a first-clear route planner for the GBA game and the Nintendo Switch Online / Nintendo Classics release. It covers major progression, upgrade order, boss priorities, SA-X handling, and completion percentage planning. It is not a room-by-room 100% item map yet.

Difficulty caveat: the route is clear, but several bosses and SA-X escapes punish sloppy movement. Save before boss doors, use Recharge Rooms when the route gives them to you, and treat late-game cleanup as a separate pass from simply reaching the credits.

Overview

Category	Route Note
Main Route Anchor	Navigation Rooms and map objectives
Main Areas	Main Deck, SRX, TRO, PYR, AQA, ARC, NOC
Ability Pickups	Data Rooms and Core-X bosses
Survival Loop	Save, recharge, absorb X, then push the next objective
100% Basis	Capacity upgrades, not major power-ups
Known 100% Targets	48 Missile Tanks, 32 Power Bomb expansions, 20 Energy Tanks
Modern Official Access	Game Boy Advance - Nintendo Classics with Nintendo Switch Online + Expansion Pack
Best First Goal	Clear the game, then use late-game tools for item cleanup

Route Walkthrough

1. Main Deck - Learn the Station Loop

Start by following the Navigation Room prompts instead of wandering aimlessly. Fusion expects you to check the computer, follow the marked objective, and return for the next briefing.

Your first Main Deck jobs are to investigate the Quarantine Bay, download Missiles from the Data Room, and fight Arachnus X. After Arachnus X, absorb the Core-X to recover Morph Ball. This is the first full loop the game will repeat: objective, Data Room or boss, new tool, return route.

Before leaving this opening stretch, get used to three habits: shoot suspicious blocks, save before boss doors, and absorb X parasites quickly. Yellow and green X are basic recovery, red X are major recovery, and boss X are progression.

2. Sector 1 (SRX) - Charge Beam and Stabilizers

Sector 1 is your first full sector route. Follow the atmospheric stabilizer objective, clear the route the computer gives you, and look for the Core-X that restores Charge Beam.

Charge Beam matters for more than raw damage. Some enemies and later boss phases are much cleaner with charged shots, and it gives you a safer fallback when missiles are low.

3. Sector 2 (TRO) - Bombs, Hi-Jump, and the First SA-X Lessons

Sector 2 introduces more layered routing. Unlock the required security level, reach the Bomb Data Room, and use Bombs to open Morph Ball paths. The major boss goal here is Zazabi X, which rewards Hi-Jump and Jumpball.

This is also where the SA-X becomes a practical route rule. Early on, do not try to win a fight with it. Hide, escape, or use the route the game gives you. If the SA-X appears before Samus has late-game tools, survival is the objective.

4. Sector 4 and Sector 3 - Speed Booster, Super Missiles, and Heat Pressure

In Sector 4 (AQA), beat Serris X to recover Speed Booster. This is the first upgrade that turns the map into a puzzle: long corridors, slopes, Shinespark setups, and Speed Booster blocks become route checks.

Sector 3 (PYR) adds heat and stronger enemies. Download Super Missiles when routed to the Data Room, respect the first Security Robot B.O.X. fight, and later recover Wide Beam from the Core-X tied to the boiler route.

Do not treat Speed Booster items as mandatory on the first visit. Mark them mentally, then return when you have the full late-game kit and enough health to practice Shinesparks.

5. Sector 6 and Sector 5 - Cold, Varia, Ice Missiles, and Power Bombs

Sector 6 (NOC) is dangerous before Varia Suit. Blue X can hurt Samus until Varia is restored, so move carefully, shoot when needed, and do not greedily absorb every X before you know it is safe.

After Barrier Core X, Varia Suit changes the cold-route rules. Sector 5 (ARC) then gives Ice Missiles, and later Power Bombs. Ice Missiles are traversal tools as much as weapons because frozen enemies can become platforms. Power Bombs are both screen-clear tools and secret-finding tools, but do not waste them while running away from the parasite cluster they create.

6. Midgame Reactor Route - Space Jump and Plasma Beam

When the station power route opens, prioritize restoring functionality and pushing the Reactor Silo path. The Main Deck boss in this stretch rewards Space Jump, which makes vertical cleanup and several later routes far less awkward.

After that, the Sector 2 plant route leads to Plasma Beam. Plasma is a major combat upgrade and sets up a much stronger late-game Samus, but the boss room still asks you to control space, avoid floor traps, and keep firing into safe openings.

7. Late Game - Gravity, Diffusion, Wave, and Screw Attack

The late-game chain is where the map opens into real cleanup potential:

Upgrade	Route Use
Gravity Suit	Freer underwater movement and safer lava traversal
Diffusion Missile	Charged missile freeze burst for route obstacles and groups
Wave Beam	Shoot through walls, floors, and ceilings, including switch checks
Screw Attack	Break Screw Attack blocks and destroy many enemies by jumping through them

Follow Nightmare for Gravity Suit, Sector 4 for Diffusion Missile, Sector 6 B.O.X. X for Wave Beam, and Sector 1 Neo Ridley for Screw Attack. Once Screw Attack is restored, many previous item locks become cleanup targets.

8. Cleanup Before the Finale

If you only want credits, keep following Navigation Room objectives. If you want 100%, pause before committing to the final sequence and sweep capacity upgrades.

Fusion’s percentage is based on capacity upgrades, not the major power-ups themselves. The known full-capacity targets are 48 Missile Tanks, 32 Power Bomb expansions, and 20 Energy Tanks. This walkthrough keeps exact room-by-room pickup locations for a dedicated item route.

For a practical first playthrough, separate the goals:

Goal	Recommended Approach
First clear	Follow objectives, take obvious tanks, save often
100% clear	Return late with Gravity, Wave, Screw Attack, Power Bombs, and Speed Booster mastery
Fast ending	Save for a later run after you know boss patterns and route locks
Under 2 hours + 100%	Treat as a dedicated speed/completion route, not a blind route

9. Finale - SA-X and Omega Metroid

The SA-X fight finally allows you to engage the copy directly. Keep movement disciplined, charge your beam, and use Ice Missiles to create safer windows when possible. The fight changes phases, so do not spend your focus only on the armored form.

At the Docking Bay, Omega Metroid is the final wall. Samus cannot meaningfully finish it until the SA-X event plays out and Ice Beam is restored. Once Ice Beam is active, fire into Omega Metroid while backing away from its claw swings. The timer matters, so prioritize clean shots over risky positioning.

Upgrade Order

Order	Upgrade	Pickup Type	Route Importance
1	Missile Launcher	Data Room	Boss doors, barriers, basic damage
2	Morph Ball	Arachnus X	Tunnels and core Metroid movement
3	Charge Beam	Core-X	Charged damage and boss utility
4	Bombs	Data Room	Morph Ball blocks and hidden paths
5	Hi-Jump / Jumpball	Zazabi X	Vertical access and ball movement
6	Speed Booster	Serris X	Speed blocks and Shinespark routing
7	Super Missiles	Data Room	Stronger missile damage and barriers
8	Varia Suit	Barrier Core X	Cold-route safety and defense
9	Ice Missiles	Data Room	Freeze enemies for combat and platforms
10	Wide Beam	Core-X	Wider beam coverage
11	Power Bombs	Data Room	Secret checks, enemy clears, orange barriers
12	Space Jump	Gedo/Yakuza X	Sustained aerial movement
13	Plasma Beam	Plant Core X	Piercing beam damage
14	Gravity Suit	Nightmare X	Water/lava movement and defense
15	Diffusion Missile	Data Room	Charged missile freeze burst
16	Wave Beam	B.O.X. X	Shoot through terrain and shutters
17	Screw Attack	Neo Ridley	Screw blocks, combat, late cleanup
18	Ice Beam	SA-X finale	Omega Metroid damage window

Boss Priorities

Boss	Priority
Arachnus X	Use wall grips to dodge rolls and fire missiles into the front.
Zazabi X	Fire upward when it opens to trap Samus, then move before it lands.
Serris X	Watch water movement and hit the head as it emerges or slows.
Security Robot B.O.X.	Use ceiling ladders and downward or diagonal missiles.
Barrier Core X	Use Charge Beam and avoid taking extra cold-route damage.
Gedo / Yakuza X	Avoid grabs, punish the mouth during openings, then finish the Core-X.
Plant Core X	Stay out of floor traps and keep pressure on the central body.
Nightmare X	Break the gravity device first, then attack the exposed face.
B.O.X. X	Stay above electrified water and shoot down/diagonal during openings.
Neo Ridley	Use charged shots or Super Missiles while avoiding grabs and tail contact.
SA-X	Freeze briefly when possible, then land charged beam shots and keep moving.
Omega Metroid	Wait for Ice Beam restoration, then shoot while retreating from claw swings.

SA-X Rules

1. Early SA-X appearances are escape checks, not duels.
2. Do not Power Bomb blindly during a stealth moment if it can expose your hiding spot.
3. Ice Missiles can buy time in some encounters, but they do not turn early SA-X into a normal boss.
4. In the final battle, charge shots are more important than panic missiles.
5. After SA-X changes form, keep reading jump arcs instead of standing under it.
6. During the Omega Metroid sequence, focus on absorbing SA-X and using the restored Ice Beam.

100% and Ending Planning

Metroid Fusion’s item percentage is about capacity upgrades. Major upgrades are required for progress, but the percentage route is built around tanks and expansions.

Completion Target	Count
Missile Tanks	48
Maximum Missiles	250
Power Bomb Expansions	32
Energy Tanks	20

Endings in the North American and European versions are tied to time and whether you reached 100% item completion. The practical split is over four hours without 100%, two to four hours without 100%, under two hours without 100%, over two hours with 100%, and under two hours with 100%.

Do the first clear for knowledge. Do a second file for 100% if you want a clean route. Save under-two-hour goals for a dedicated run after you know which item checks waste time.

Nintendo Classics Notes

Nintendo currently lists Metroid Fusion in the Game Boy Advance - Nintendo Classics library for Nintendo Switch and Nintendo Switch 2, with Nintendo Switch Online + Expansion Pack required.

The Nintendo Classics app supports save-anytime and rewind, with rewind available by holding ZL + ZR. Use those features for practice, especially on SA-X escapes, Shinesparks, and late boss patterns. Exact button labels and Switch 2-specific behavior can depend on the app and hardware you are using.

Common Mistakes to Avoid

1. Skipping Navigation Rooms - You can miss the active objective and waste time in locked routes.

2. Trying to fight early SA-X encounters - Run, hide, or follow the escape path until the finale.

3. Absorbing blue X before Varia Suit - They can hurt Samus before the cold-route upgrade is restored.

4. Leaving Core-X pickups uncollected - The exposed boss X is the ability reward.

5. Spending Power Bombs while moving away from the blast center - Stay near the detonation point when you want the pulled-in X recovery.

6. Treating Speed Booster rooms as one-visit checks - Many Shinespark items are cleaner after late-game movement upgrades.

7. Entering boss rooms without saving nearby - Several bosses can punish one bad pattern read.

8. Starting 100% cleanup too early - Wait until Gravity, Wave, Screw Attack, Power Bombs, and Speed Booster options are all available.

9. Ignoring Energy Tanks before SA-X and Omega Metroid - Extra capacity gives you more room to learn the final sequence.

10. Assuming the ending is only time-based - Item percentage changes the ending category too.

Frequently Asked Questions

Q: Is Metroid Fusion fully open like Super Metroid?
A: No. It uses mission objectives and Navigation Rooms for most of the game, with broader cleanup later.

Q: What counts toward item percentage?
A: Capacity upgrades count toward percentage. Major power-ups are progression tools, but they are not the percentage pickups.

Q: Should I chase 100% on a first run?
A: Only casually. Take obvious tanks, but save full cleanup for late game or a second run.

Q: Can I defeat the SA-X early?
A: No. Treat early appearances as escape and stealth sequences.

Q: Is Nintendo Classics rewind part of the original game?
A: No. It is a wrapper feature for the current Nintendo Classics app, useful for practice but separate from original GBA mechanics.

Summary

Category	Top Tip
Route	Let Navigation Rooms define the next objective
Upgrades	Track Data Room downloads and Core-X rewards
Combat	Absorb X for recovery and boss rewards
SA-X	Escape early, fight only when the finale allows it
Completion	Count tanks and expansions, not major power-ups
100% Timing	Clean up late, after the full movement kit
Nintendo Classics	Use save-anytime and rewind for practice, then check exact app behavior before relying on them