Tourian is as close as Metroid comes to having “levels” in the traditional video game sense. You make it through the gauntlet of Rinkas and Metroids a screen at a time and arrive at last at the boss. Even the doors in Tourian say “serious business” — they’re orange instead of red, soaking up ten missiles instead of five. The only other door in the game like that was the one behind Ridley. The message is clear: Every time you reach a door in this area, you should experience the same sense of elation you feel when you’ve just beaten a boss.
Behind the final door, the boss room awaits. And, you know, the idea of a “boss room” has become a real cliché in games. Even here in Metroid in 1986 we saw both Kraid and Ridley situated in strange, stark chambers where they did nothing but sit in wait for the hero to come blow them up. It’s kind a goofy concept if you stop to think about it; how miserable must that existence be, lurking in the dark with nothing to do until some do-gooder comes along to blow you up? You never see proactive villains in action games like this — though this very franchise made a brilliant and terrifying exception to that rule in its fourth installment — just slobs who sit and wait until the good guy finally gets through the deadly-but-not-too-deadly gauntlet leading up to them.
In Mother Brain’s case, however, this actually makes perfect sense. She’s a biological computer, and as such this is basically her server room. She’s totally immobile, powering Zebes’ systems or whatever from the safety of Tourian’s deepest sanctum, just like you’d expect a computer to do. And what she lacks in direct firepower — the Mother Brain is completely harmless unless you bump into her — she makes up for with supporting defenses.
Mother Brain’s lair is a single lengthy room divided internally into six different chambers by five Zebetites, which appear to be conduits or defensive barriers or something. Like Mother Brain, they’re biomechanical, meaning they possess regenerative capabilities. Each one takes several missile blasts to destroy, but if you don’t pour on the steady fire they quickly grow back — you can gauge your progress, not to mention the ground you’ve lost, by the condition of a Zebetite. They start thick and slowly dwindle in diameter to vanishing as they take damage, growing back to full width if you don’t destroy them quickly.
Like Mother Brain, a Zebetite also can’t attack you directly. However, taking them out is anything but a cakewalk, because each one is elevated high off the ground with only a narrow platform adjacent to give Samus a clear shot. The problem is that while you’re doing this a trio of guns is rotating and firing energy beams at you in a not-quite-random fashion. And, on top of that, Rinkas are spawning rapidly from every direction.
Despite the final boss’ lack of a direct threat, this is an extremely challenging sequence. Taking down the Zebetites burns through your stock of missiles quickly, and because Rinkas don’t drop energy pickups and Metroids only respawn when you die and continue, you’re stuck fighting with what you have on-hand. [Edit: Or maybe I’m wrong about this, but still — tough sequence regardless.] It’s a battle of attrition, a test of how effectively you can dodge the threats surrounding you and pour missile fire into your targets. The developers do demonstrate a surprising touch of mercy here, though: Once you destroy a Zebetite, it’s gone forever. Like the minibosses, Mother Brain’s energy conduits don’t regenerate if you see a game over. In a worst-case scenario, you can fight your way through this chamber one Zebetite at a time, constantly restarting and fighting your way back, delving a little further into the room each time.
The further you get into the room, the more difficult it becomes. Around the time you hit the lava, it just gets ridiculous. Don’t computers need cold to work more efficiently? Shouldn’t Mother Brain’s server room be, like, super refrigerated? Pfft.
Really, this room can be as difficult or as easy as you like. The gun turrets follow fairly predictable patterns — some shoot at 90-degree angles, while others fire 45-degree-angle shots — and while the Rinkas materialize from all over the place and home in on Samus’ location as of the second they spawn, they obey the same strictures as they did during the Metroid gauntlet. Specifically, there will always be a fixed number of them on-screen at any given moment, so if you freeze one it’ll take that particular spawn out of play.
It’s actually not too difficult to deal with the Rinkas while destroying the Zebetites, because each column has solid footing directly below it that allows you to skip the blue platforms and jump up and down right in front of the Zebetite, firing several point-blank missiles per leap and wearing down the Zebetite in short order.
Mother Brain herself, however, is considerably more difficult. Once you shoot out the glass case surrounding the computer, you need to pump more than 30 missiles right into her face (and they have to hit dead-on or they won’t cause any damage). Unlike the Zebetites, her health doesn’t regenerate if you lay off your assault for a moment. That’s about the only saving grace, however.
The most sensible place to attack Mother Brain from is the Zebetite junction directly in front of her — the blue platform further away works as well, but it’s constantly targeted by both Rinkas and gun emplacements — yet this leaves you incredibly vulnerable. Rinkas spawn constantly above and below you, and if you’re hit there’s an awfully good chance the recoil will send you flying into the lava directly in front of the glass chamber. The wall to the right is slightly too high to reach while jumping out of liquid, and if you try to use Mother Brain’s platform as a foothold you’ll take damage from proximity to the boss and be sent flying right back into the lava. The only reliable way out is to freeze a Rinka and use it as a foothold, but that’s pretty difficult while you’re being harassed by several others at the same time. The moral of the story: Don’t let yourself be knocked into the lava.
Because there’s no time crunch here, the smartest thing to do is to take your time. Drop back and freeze the Rinkas, giving yourself a short window of breathing room. But this tactic is slightly counter-intuitive to the design of the entire room; because the five Zebetites leading to Mother Brain required a rapid volley of missiles, your brain is still in “frantic” mode when you finally reach the boss herself. You actually need to stop and recalibrate your approach here.
With smart play and the good sense not to fall in the lava, you can eventually best Mother Brain… even if you have to keep dying and retrying to do it. But once that happens, the absolute trickiest part of the game begins.