10. Quadraxis (Prime 2: Echoes)
It's a big ass robot. That by itself already gets some bonus points right there. The fight itself is very long, some parts are a bit obscure in terms of how to deal damage and honestly it can get kinda annoying. I wasn't a big fan of this one the first time, but it has proved to be a memorable fight and it feeling almost like an endurance test is a big reason why. You really got a sense that this thing wouldn't go down easily, because well, it shouldn't.
9. Crocomire (Super)
Croc has to get in. Such a memorable fight, easily the most iconic non-major boss in the series. A rare one in that doing damage isn't exactly how you beat it; this one can be a real struggle on the first attempt but once you get used to it it's kind of a cakewalk. Also I love just how brutal the death scene was, and also love the fake out at the end. I'm always down for weird unexpected moments like these because it creates a lot of tension and uncertainty. Super Metroid excelled at that and Crocomire was one of its best examples.
8. Mother Brain (Zero Mission)
Zero Mission has a big issue of being too easy with its boss fights, but here it had a bit of an opposite issue where this boss was a major difficulty spike. It wasn't very well-balanced, but it was a really cool challenge and great recreation of the original fight on the NES. Just like in the original, this is all about finding the right time to shoot missiles while trying to dodge a seemingly endless barrage of projectiles. Unlike the original, this one doesn't just kill you for falling in the pit and also it doesn't run at like 2 fps. It's just great. I kinda wish the game ended here, but alas.
7. Proteus Ridley (Samus Returns)
It was about halfway through Samus Returns that I had a sudden realization that Ridley was gonna be tacked on at the end. It just felt so obvious. I have mixed feelings on this one, because story-wise it's really stupid, and it completely destroys the original game's peaceful ending - while also making the real final boss, Metroid Queen, feel a bit irrelevant. I'm also not a fan of how many cutscenes they threw into this fight, it all just felt so forced. But. Holy crap this fight was epic and insane and awesome? It was really cool seeing Ridley as a final boss for the first time, even if he shouldn't have been, this was just really cool. The battle felt totally wild and brutal, as it should be with Ridley.
6. Nightmare (Fusion)
Fusion spends a good time foreshadowing this guy, and it's some really incredible foreshadowing, but it kinda makes you feel like the fight couldn't live up to it. But it does. The moment Nightmare starts messing around with gravity is the moment you feel like you're in deep shit. Shoot a missile, and it just drops to the ground like it's nothing. Having to stick to this little ladder on the wall while it approaches you is really scary, and makes you feel kinda helpless. Just a really iconic boss.
5. Mother Brain (Super)
Everyone and their mom has seen this one. It's kinda pointless to even start explaining why it's so great, because everyone knows why. It's just really poignant, a perfect climax for a near perfect game. That said, gameplay-wise this one's kinda lacking, it's very much on the easy side, hence why it's not higher on the list. Apart from the first phase, which is just an easier version of the NES/ZM Mother Brain, it plays almost like a cutscene. Still, you can't not list it. Such a powerful moment.
4. Meta Ridley (Prime 3: Corruption)
This fight was absolutely ridiculous and I love everything about it. It had some great foreshadowing as you see Ridley flying around and causing chaos throughout your mission on Norion - and he always shows up in the middle of gameplay instead of in cutscenes, which makes it even more memorable. Despite the foreshadowing, though, the battle starts in a very abrupt and unexpected way, and what then ensues it total madness. Both Samus and Ridley falling down the Star Wars shaft in their usual wild battle to try and brutally kill one another, without giving a shit about the fact that they're both likely to die in this scenario. Having the altitude displayed as a timer of sorts only helps to make this one feel even more epic than the premise by itself already is. I just think the way it ends, with the ice guy from The Incredibles showing up to save you, is pretty anti-climactic and disappointing given how awesome the boss is. A shame most of Prime 3's other bosses are awful.
3. Ridley (Super)
This one's just genius. We take it a bit for granted nowadays, but I think Super Metroid is where Ridley really established himself as a truly iconic villain. Everything about his appearance in this game was so well-made, everything, from start to finish. All the dead bodies in the opening, the stolen Metroid, then you see it's him - and you can't do anything about it. Ridley plays with you until he gets bored and leaves. Then the whole game's just about trying to find him. Halfway through the game you're likely to stumble upon a Ridley-like door, but you can't get in until way later. When you do get in, you're greeted by some very climactic music and a place that looks and treats you like hell. At the end of it all, Ridley appears again, in the same way he did in the beginning... but this time, the fight's gonna go on until one dies.
The battle itself is also fantastic. This is one of the rare examples in a Metroid game where a boss has a proper AI - he'll react to your movements and choose his attacks accordingly instead of just performing pre-determined patterns. He'll fly around the room shooting you from distance and constantly moving out of your line of sight, which along with his positioning-based AI really makes this fight feel more about the movement than the shooting. You gotta know when to jump, when to run, where to move towards, and when you get good at it, it's almost like a dance.
Once his HP drops down to 0, which takes a while to happen, Ridley unlocks a new move: dying. This means he doesn't just die immediately after a certain amount of shots - instead, he'll stay alive until either you get grabbed, or whenever he just decides to explode. It's fitting for the "cunning god of death" to just choose when to die, but more than that, it makes this fight really intense for a first-time player, as no matter how many E-tanks or Super Missiles you have, you're likely to get to a point where you'll feel in danger of dying. And that's just awesome. Maybe not as awesome that the save point is so far away from him, but in a way that makes this even more memorable. And after beating Ridley, there's no Metroid to be found...
2. Meta Ridley (Prime)
The moment Metroid Prime solidified itself as a masterpiece. The game knew how to raise the stakes for its final areas, certainly in Phazon Mines, and as you approach the endgame the tension was palpable. Suddenly, Ridley. This takes a lot of inspiration from Super in how it foreshadows him throughout the game, but when he drops down to attack you at the Chozo temple, all inspiration is thrown out the window in favor of a very original and very, very iconic battle.
I don't even know how to begin describing this one. Everyone who's played Metroid Prime knows just how unforgettable this boss battle was. I'll just say it has the best rendition of Ridley's theme and leave it at that.
1. Metroid Prime
And following on from Meta Ridley's very violent death scene, the tension only gets even more intense when you enter the Impact Crater. There is something impossible to describe about Metroid Prime's late game atmosphere, it's just so ominous and really gets your heart racing. Enter the titular character.
This is what a Metroid final boss should be like. Properly stressful and climactic. Requires you use a wide variety of skills you got over the game. A long test of endurance and challenging battle. It looks gross and disturbing. And it's the root of all of Tallon IV's corruption. This is how it should be.
For me, it was just unforgettable the first time. Died on my first attempt near the end of the first phase; barely made it through the battle on the second attempt, with the "Energy Low" warnings beeping everywhere at the end. For me this was one of the most intense and most awesome boss fights in any game, I don't think that'll change.