Tourian is a very linear area where all runs must converge into this area at some point after defeating Kraid and Ridley in order to progress through the game. Once you've entered Tourian, all runs of all categories will be taking the same path to kill the Metroids, kill Mother Brain, and complete the post-game Suitless section afterwards and defeat Charlie. Tourian does have some unique strats that are different in Any%, 100%, 9%/10%, and Hard mode also makes this section very different because it greatly increase the number of Metroids and they all kill you much more quickly.
Ammo management is a top priority throughout all of Tourian. Each Metroid must be frozen with the Ice Beam before it can take damage, and it takes either 5 regular Missiles or 1 Super Missile to kill a Metroid. This is the only way a Metroid can be damaged and killed, making Ice Beam and Missiles a requirement to clear even the first Metroid room. If you're coming from Super Metroid and are expecting Powerbombs to do anything to a Metroid, they do not. This really doesn't matter in Zero Mission because you can't even acquire Powerbombs before entering Tourian anyways.
Drops are very random and very important to manage as well. Each Metroid will drop two drops which can either be a regular missile, a large health drop, or a super missile. If you are doing a category where you do not pick up any supers before Tourian, you may see small health drops, which is what happens when the game was going to give you a super drop but had to change the item to the next available item in its "drop list" because supers aren't available.
If you get grabbed by a Metroid, the only way to remove it is by laying a regular bomb and having the explosion hit the Metroid. The safest way to do this is to just sit still and lay one bomb, let it pop the Metroid off so you can see which way the Metroid goes, and roll in the opposite direction. If you're high up in midair and don't have time to land before the Metroid kills you, you can morph in midair and lay a bomb, and then quickly unmorph which should raise the Metroid into the explosion and knock it off of you.
There are 4 Zebitites (the breakable red walls) in Mother Brain's room. Each Zeb takes 7 missiles to break, or one super + 2 regular missiles, and all missiles must be fired rapidly into the Zeb. The Zeb's will regenerate their health if you stop shooting them, so if you get knocked around by the turrets or rinkas and miss some shots, it can end up costing you even more ammo to finish off the Zeb. It is possible to clip through the first Zeb using the Zeb Skip, which also prevents the third Zeb from spawning, meaning you only need to destroy the 2nd and 4th Zeb's if you can pull off the trick.
Mother Brain's glass tank takes 20 missiles to break, and Mother Brain herself takes 35 missiles to defeat. Doing the math means you need 83 missiles to defeat all 4 Zebitites and Mother Brain without stopping to refill any ammo. In a typical run you will likely have 4 Super Missiles saved for Mother Brain which lowers the number of required regular missiles down to 63, and if you're performing the Zeb Skip and skipping two of the Zebitites this number is further lowered to 49 regular missiles to complete the room without farming.
In a typical Any% run you will enter Tourian with 50 Missiles and 4 Super Missiles. You will want to alternate between using both types of ammo, because Super drops are pretty rare you will want to use your Supers early so that you don't "waste" a Super drop. If you're maxed out on Supers and get a Super drop, you not only waste it by not gaining any Super Missiles back from it, but you also waste regular missiles because you've spent 5 regular missiles to get the kill and didn't get any back.
Others may want to update this guide in the future with their strategies because everyone does Tourian differently and for different reasons, but my rhythm is as follows:
- Stand on the left side of the first Metroid and Super it to leave the room as fast as possible.
- Drop down in the 2nd room and missile the first Metroid because you have to wait for the 2nd Metroid anyways. Super the 2nd Metroid once it's above you, jump into their drops and leave.
- Kill each individual Metroid in the 3rd room with missiles, if you get any super drops you'll want to save them for the 4th room. It is possible to run past the Metroids if they have a slow spawn and kill them in two groups of two, but it's debatable if this even saves time and is more likely to mess up your rhythm and cause mistakes.
- In the 4th room do a small jump into the lower area, this jump will trigger the 3rd Metroid to spawn off screen in the top area. Run to the right and wait for the first two Metroids to spawn. Kill all three Metroids with supers from that bottom right corner, jump up and kill the 4th Metroid and leave.
- In the 5th room just run through the room and kill each Metroid as it spawns. When you get to the last bottom area with two Metroids, it's pretty safe to land all the way at the bottom and kill the very last one while you wait for the 2nd-to-last Metroid to spawn and come down to you.
- In the last room with the breakable floors, you want to start on the right side and kill the Metroids in groups of two at a time.
In the last hallway before the Zebitites you will want to use your speedbooster to reach the end of the room and open the red door quickly, and then farm the green rinkas to max out your ammo. The red rinkas only have a chance to drop something, while the green rinkas are at least guaranteed to drop something, even though they don't always drop what you need. If you're doing the Zeb Skip you will want to farm up to max missiles and supers and go fight mother brain. If you're not doing Zeb skip, you only need at least 14 missiles to run into the next room and kill the first two Zebitites, then you can return and farm back to maximum ammo.
Eventually you should reach Mother Brain which has its own guide, and after the fight you will escape and complete Tourian.
In a typical 100% run you should enter Tourian with plenty of ammo and be able to clear all the rooms without stopping. The general ammo strategy for 100% is to never go below 4 Super Missiles in your inventory, but always use supers if you have more than 4. It is much faster to fire one super missile to kill a metroid than firing 5 regular missiles, so a very lucky run will get a bunch of super drops and use only supers for the entire area. This luck is not very likely to happen, so what usually happens is you will drop down to 4 supers and have to use regular missiles while you hope for a lucky super drop. With the amount of ammo you pick up in a 100% run, plus the amount of regular missile drops you should be getting if you're not getting super drops, you should never have to worry about running out of missiles before the Zebitite room. You should be able to run straight into the room without farming and shoot all the zebs, and if you get really lucky and have more than 4 super missiles you can use your extras to break the glass faster. Once you reach Mother Brain herself, it's the same fight as Any% and afterwards you will escape and complete Tourian.
Tourian is one of the scariest parts of 9% runs for two reasons: It's very easy to die very quickly and very unexpectedly which can kill your run, and even if you're comfortable with not dying it is still very possible to get screwed with unlucky drops and lose all your time just from bad RNG which can also kill your run. In normal mode you will only have 5 regular missiles and no extra etanks. Getting grabbed while at full health means you will die within a couple seconds, and getting grabbed with any less than full health almost always means instant death.
With the best case scenario each Metroid will hopefully drop two missile drops for a total of +4 missiles, so you still need to farm a 3rd drop from a rinka to kill more than one Metroid. You don't always want to immediately pick up that third drop, because instead of getting +2 missiles you will only get +1 missile and reach your maximum of 5. So for this reason, the general strategy for each pair of two Metroids should be:
- Spend all 5 missiles to kill one Metroid, hopefully get 4 missiles back from its 2 drops.
- Shoot all 4 missiles at the next Metroid, keep it frozen while you farm a drop from a nearby rinka
- After one drop, fire one more missile to kill the Metroid and (hopefully) get +4 more missiles from it to bring you back up to 5.
The Zebitites are a new kind of trouble because you need to fire 7 continuous missiles into each Zeb to break them. The only way to do this in 9% is to lure the rinkas nearby and destroy them in places where you can run into their drops. Keep destroying rinkas until one of them drops a missile drop, then you just have to time your shooting so that at some point after firing at least two missiles you can run into the drop and get all 7 shots into the Zeb. If you do the Zeb Skip trick you can save time by skipping two of the Zebitites.
The Mother Brain fight is pretty involved so I'll just refer to the 9% section on that page for that fight. After the fight, you do the usual escape with a required Infinite Bomb Jump to get around the final speedbooster blocks.
In Hard Mode all of the strategies have the same general principal for each of their categories, but the major difference is after the first Metroid room you will find every Metroid room has a lot more Metroids in it, and they all do double damage which can kill you very quickly even in a 100% run. Low% hard mode runs are even more intense because you will have even less ammo to deal with the extra Metroids, it really just requires a lot of practice to get comfortable with where they all spawn and where you want to farm the rinkas.