Arachnus X
Location: Main Deck
Prize: Morph Ball
Bio: If you've played Metroid II, this dude is from it; in fact, Arachnus was one of the only two bosses in that game. However, this iteration proves to be different, likely because it's an X host. It attacks with sharp wave slashes and rolling into a ball to tackle you. After killing it, you fight it's Core X, something you should get used to when fighting bosses in Fusion from now on. There are two types of Core X: Membrane cores, that which you only have to hit with missiles anywhere, and eye cores, that which can only be damaged if you shoot a missile into its eye. When the Core X is destroyed, you absorb it (thanks to the Metroid vaccine) and obtain the Morph Ball.
Fake Chozo Statue
Location: Sector 1 (SRX)
Prize: Charge Beam
Bio: At first, it's a Chozo statue. Shoot the item stone to reveal the Morph Ball power-up. However, the statue then turns immediately into an eye Core X. Bust the membrane by shoving missiles into its eye, and absorb the X. You just obtained the Charge Beam.
Zazabi
Location: Sector 2 (TRO)
Prize: Hi-Jump and Jumpball
Bio: When on the ground, Zazabi cannot be damaged. However, soon Zazabi starts hopping around mindlessly, soon to slowly hover down with its mouth open. This is your time to shine. Shove a few missiles into the mouth for it to reach the eye. Soon, the mouth gets smaller, and Zazabi glides down faster. Simply continue the process. Should you get swallowed by Zazabi, use Bombs in Morph Ball form to force yourself out. Zazabi soon turns into a membrane Core X. You know what to do. The remaining core is red and blue; this is because absorbing it will give you two of your abilities back: Hi-Jump and Jumpball.
Serris
Location: Sector 4 (AQA)
Prize: Speed Booster
Bio: Serris is, according to A-er, the computer, a serpent that can attack at ultra-fast speeds. Which explains the Speed Booster. Now, after doing some calculations, the Charge Beam actually works better in this game. Both missiles and the Charge Beam will send this creature into hyperspeeding fury, and since one missile will piss it off, and missile < Charge Beam, you should be aware of what you choose. Serris moves around similar to how Botwoon snakes around in holes. When it's slowed, hit its head with a charged shot. It will start to go crazy in hyperspeed, and I know how to dodge this. Enter the water. Stay in Morph Ball mode towards the left of the room, but not all the way left. Serris is sneaky, and sometimes pops out directly next to the door, so only go towards the left. Serris never touches that spot, so you're good to go. When it comes back to normal speed, hit it with a charged shot, and rinse and repeat. Serris will become a membrane Core X, and absorbing it gives you the Speed Booster ability.
B.O.X. Security Drone Battle 1
Location: Sector 3 (PYR)
Prize: None
Bio: This fight...hm...let's just say it will either be extremely difficult, or pathetically easy. It just can't be in between. But anyway. The drone can only be damaged by its head, which is entirely protected by heavy duty armored arms. You can hang onto the monkey bars above to make the fight easier. All the drone does is jump around, and shoot bombs that will raise walls of fire in both directions. Here's a tip for avoiding getting hit by the bombs' impact: when it's shot out, go directly above it. Yeah, call me crazy, but that's how it works. The impact doesn't go straight upward, but rather the walls of fire extend outwards in both directions as said. If you couldn't reach the bomb in time to climb directly above it, then wait for the fire to retract, and quickly climb over it during recession. The walls of fire retract low after a short bit, then extend again shortly after. So be very cautious. After you've damaged the drone enough, it will hop away, leaving debris behind, allowing you to climb upward and escape this sector.
Megacore X
Location: Sector 6 (NOC)
Prize: Varia Suit
Bio: This boss doesn't really inherit the Varia Suit's abilities, but anyway. When you reach the data room in Sector 6, you'll find a Core X absorbing the Varia Suit's abilities and destroying the data room. Continue into the large room with water. The large Core X forms an even stronger shield that can only be damaged by charged shots, and surrounds itself with smaller variations of itself as well. Simply a few shots will force the shield off, and you will fight a membrane Core X. Absorb the X after so to get the Varia Suit!
X Infected Scientist
Location: Sector 3 (PYR)
Prize: Wide Beam (what was once called the Spazer)
Bio: Like the fake Chozo statue, this fight is pretty simple. You're sent here because something is telling the main boiler in Sector 3 to melt the entire sector, which, according to the computer, could make the entire B.S.L. Station exlplode. You have six minutes to get to the boiler, and when you do, you see a bald scientist fiddling with the controls of the boiler. Shoot him a few times to make him revert into an eye Core X. Ah, haven't fought one of these in a while. Hopefully you know what to do. Absorbing it will give you the Wide Beam, which is the equivalent to the Spazer. After this, fix the controls of the boiler, and the sector will cool down.
Yakuza
Location: Reactor Silo
Prize: Space Jump
Bio: Well, well, as it turns out, something stopped the power in the entire station, and you have to restore auxilary power, for starters. And you end up fighting Yakuza, a large spider boss. Brace yourself for this one, and perhaps sigh in relief. This is actually one of the hardest bosses in the game. After this, you're good to go until SA-X. How do you kill Yakuza, you ask? What? It just keeps picking you up and taking out waaaaaay too much energy? Oh yeah. That's what it does, plus shoots fireballs. You can't avoid the fireballs as easily, but the picking up part is entirely avoidable. Enter Morph Ball, and stick yourself in a corner. Now, the freak can't touch you. Clever, eh? However! I suggest you stay on your toes, and watch for when Yakuza is about to spit fireballs. When his mouth opens, shoot missiles into its mouth (missiles prove more useful in this fight, because you can fire rapidly into its mouth). Get out of the way of the fireballs, and stick yourself back in a corner in Morph Ball mode. Shortly after, Yakuza will lose its legs and start hopping in mid-air, spitting unknown material out. Stand in one corner of the room and fire missiles diagonally. Spam R+B constantly when Yakuza hops near. Shoot into its mouth multiple times, and then prepare for a membrane Core X fight. Breeze through that part, absorb it, and you now got yourself the Space Jump!
Nettori
Location: Sector 2 (TRO)
Prize: Plasma Beam
Bio: Ah, Sector 2, how long it has been. Unless you've been goofing off, you haven't been here since Zazabi! But anyway. This fight is easy, but annoying. At first, it will partially behave like Spore Spawn. Little flowers up high shoot spores at you, and unless you're good on your feet, you'll fall into an energy sucking flower, which believe me, is annoying. Your target is the large golden Chozo statue being infested with vines. Shoot missiles into the statue, and soon, the front part will fall off. The spore-spitting flowers disappear, and the Chozo statue - with its front entirely blown off - will start shooting plasma shots at you. These are very easy to dodge. Continue the fight as you've been. When the statue is annihilated, you'll fight an eye Core X, which will provide you with the Plasma Beam!
Nightmare
Location: Sector 5 (ARC)
Prize: Gravity Suit
Bio: Remember when you first came to Sector 5, after getting the Ice Missiles, and when you were avoiding Chute Leech/Hellfish hybrids, there was an odd silhouette zipping around behind the glass, making an eerie sound? That was Nightmare. Now, you're actually fighting it. Nightmare was apparently a failed military drone supposedly built for use in battle against the Space Pirates. It specialized in manipulating gravity. How it failed, I have abso-freaking-lutely no clue, because this is a rather hard fight, unless you spam B while holding R. But anyway. Begin the fight by getting under the fiend and shooting missiles at its gravity manipulator. It sticks out. You can't miss it. It doesn't take much to force Nightmare to start up its special device. When it does, it's an exact replica of being underwater. Except now, missiles are uneffective, as the gravity pushes on them to the ground. Unless, of course, you fire them point-blank into the device. Use charged shots instead, however. A few shots will destroy the manipulator, causing gravity to return to normal, and Nightmare's mask to blow off. The face under Nightmare's mask is disturbing, so I won't describe it. Climb onto the wall bars and start rapidly firing missiles into the drone's nasty face. It now likes to ram you more often, for some reason. Simply use Space Jump to try and avoid. When Nightmare floats to the opposite side of the room, hop onto the monkey bars. It should trigger his AI to command him to float slowly towards you while shooting his lasers. Hold R and spam B into its face, mercilessly. If done with great timing, you should be able to force Nightmare into its Core X form in two rounds. Absorb the core, and you will obtain the Gravity Suit!
B.O.X. Security Drone Battle 2
Location: Sector 6 (NOC)
Prize: Wave Beam
Bio: What's this? You came to some gate that implies that you aren't authorized to progress! What's up with that? You have clearance to go to all sectors!...Ah well, better turn back. Wait, wtf? When you come a few rooms back, the familiar face returns. This time, it's in a pit of water, making the liquid dangerous to the touch. The armor on its skull is almost blown off, leaving just a glass case and an organic brain underneath. This surely sounds familiar, doesn't it? Yeah, well. Use a Power Bomb to reveal a set of monkey bars to hang on. The drone has a new weapon, replacing the old bombs: heat-seeking missiles. This time, the drone can knock you off the bars by jumping, so you'll end up in electrified water. Here's a nice technique to use: Go to the far right of the room, and hang on the monkey bars. Go the furthest right on the bars as possible. If you initiate this tactic with good timing, this battle should be a breeze. The drone's AI commands it to release missiles every few jumps, and if you initiated the tactic at the right time, it will always unleash them in the same spot. Destroy the missiles by shooting them. It will then walk towards you, following with a jump, trying to knock you off, but a short ledge prevents it from reaching you. When in your weapon's path, fire multiple missiles. Rinse and repeat. When the glass case is destroyed, the robot will revert to an eye Core X, and the water won't be electrified. Finish the Core X, and absorb it to get...the Wave Beam! Remember that gate that said you weren't allowed in? Well, that's because the shutter's release button was on the other side, making it unreachable...but now, the Wave Beam can penetrate walls, so why not use it to "sneak" into there, just to check things out?
Ridley X
Location: Restricted Zone
Prize: Screw Attack
Bio: I won't spoil what was in the lab. But after you're done exploring the "Restricted Lab" you supposedly weren't allowed into, you're released into a mechanical lab connected to Sector 1. In this lab, you fight the grossly distortionate and pathetically easy Ridley X. If you were curious what was in the subzero containment room nearby your ship (guilty as charged) and went there when you got the Varia Suit, you would've seen Ridley there, frozen solid. Well, he got free. But the X copied his genetic code and made him into this ugly...thing. It's just like Ridley from Zero Mission, only loads slower and easier. And less fireball spitting. Use charged shots to finish Ridley faster. Beating him and the membrane Core X that follows will earn you...the Screw Attack!
SA-X
Location: Operations Deck
Prize: None (for the moment...)
Bio: Gracious. Goodness. Gracious. Overpowered beyond all things possible, this thing is a real *******. If you made the mistake of not trying to get all Energy Tanks (aside from if you were attempting a speed-run) before this, you will likely die. The only things that damage it are your Screw Attack and a charged shot. That's it. All it does is shoot its Ice Beam at you, and Screw Attack. If it does a Screw Attack, go ahead and run. But keep a shot charged for when it lands. One Ice Beam shot will knock out two Energy Tanks or so, and the Screw attack isn't much better. Twenty direct charged shots or so will supposedly defeat the fiend, up until it transforms into a hybrid of Samus and a Hornoad. Remember at the beginning, the Prologue, when Samus got infected by the X within that Hornoad? That Hornoad DNA remained. But this phase is actually pretty easy. All it does is try to jump on you, and you defeat it by hitting it with four charged shots. It will then revert to its Core X, which is an eye Core. Beware, this eye shoots the Ice Beam as well. Destroy it as you have with all other eye Core X's, and soon, the prize is yours!...or not. It flies away before you can grab it. Oh well. Back to the mission. Turn on the self-destruct mechanism, and hurry back to your ship.
Omega Metroid
Location: Docking Bays
Prize: Credits
Bio: It just seems to me that this is a replica of the fight against Mother Brain II. Except they tried to make it as good, though it wasn't, but this fight was actually pretty nice. The Omega Metroid isn't too hard, but it's damn powerful. You get to the dock where your ship should be, and you also see an extremely large Metroid shell. After a few seconds, an Omega Metroid pops out, and slashes you. It was so powerful, that you lost all health but one HP. The SA-X's core then comes in and starts shooting the Ice Beam at the Metroid's belly. It takes damage, and then slashes at the SA-X. The SA-X reverts to its Core X, only without a membrane. Grab the core, and your health will get restored. Your entire suit will turn orange, and you will earn the Ice Beam! Go under the Omega Metroid and shoot the Ice Beam constantly. It will slash, and kill one Energy Tank of yours, plus leave you panting for a second. Keep on shooting its belly. If you decide to be a coward, the adult Metroid will corner you and take out three Energy Tanks. So, keep up your assault. Oh, have I mentioned, you had three minutes to escape the station since you destroyed the SA-X? Yeah, well, that still stands strong. 'Cept now, you prolly got, what, a minute and a half, maybe? So you'd better hurry. Killing the Omega Metroid in time will call your ship to the docks, and you will escape safely. Congratulations, you've beaten the game!