Alright, I'm using the information from Nintendo's official book, so any mistakes I make are not my fault. The book is rather faulty, so I assume there will be a mistake or two...
Now, in this guide, I will help you defeat the Pokémon Emerald Gym Leaders. So, from Gym's One to Eight, there will be a full battle strategy for you to use. And seeing as I'm so nice, I'll even add in a guide for the Elite Four!
Gym Leader No.1, Roxanne:
Now, Roxanne uses the Rock type. So, firstly, here's the list:
Geodude: Rock/Ground types. Level 12
Geodude: Rock/Ground types. Level 12
Nosepass: Rock type. Level 15
So, there are two different battle styles open...
Firstly, you may be lucky, and you might have chosen a Treeko, or a Mudkip. And if you chose Torchic... Well, good luck. So, here's strategy number one, if you chose Treeko, or Mudkip.
So, you have chosen either Treeko, or Mudkip, thus giving you an advantage, with your type being super effective. So really, you just have to use either, 1, Absord, when you're a Treeko, or 2, Water Gun, if you'rea Mudkip. So really, it's very simple, and you should last.
For choice two, you have picked Torchic. Now, what I reccomend you do, is fight all of the people in the gym, and try to evolve. Once you gt Double Kick, you should be fine. If you try and take out Roxanne without it, then good luck. Perhaps if you spend all your money, but items, and deposit them, then you can battle Roxanne over and over again, until you get to a high level.
Gym Leader No.2, Brawly:
Now, Brawley uses the Fighting type. So, firstly, here's the list:
Machop: Fighting type. Level 16
Meditite: Fighting/Psychich types. Level 16
Makuhita: Fighting type. Level 19
Yet again, there are two battle Strategies open. One is risky, but effective, and the other is safe, but can be dangerous, if it takes too long.
Firstly, the risky strategy.
Now, if you leveled up your Torchic into a Combusken, then you should have Peck. Now, by using Peck, you should wipe the opponents clean, unless Meditite uses Confusion. And that, my friends, is not what you want. Oce you beat Meditie, it should be easy to take out the Makuhita.
Now for the safer, but less effective, strategy.
As a Treeko or Mudkip, none of Brawley's Pokemon have a super effective hit on you. So really, you can stall with Mudkip and Mud Slap, as the loss of accuracy will really hurt Brawley. And as for Treeko, you should just use Absord, as that will provide an easy win.
If you are having some trouble, I reccomend leveling up in the cave, just to the left of the city.
Gym Leader No.3, Watson:
Now, Watson uses the Electric type. So, firstly, here's the list:
Electike: Electric type. Level 20
Magneton: Electric/Steel types. Level 22
Manectric: Electric type. Level 24
Voltorb: Electric type. Level 20
Now this Gym should be a breeze. However, there are two different approches you can take towards this Gym.
The first when is nice and simple. By now, you should have Evolved your starter Pokémon by now, as once you get Mudkip and evolve it into a Marshtomp, it will not be effected by Electric attacks, rendering Watson useless. Then, you simple attack with either Water Gun, or Mud Slap. Now, if you have a Combusken, you can simply Ember and Double Kick Watson's Pokémon.
This Gym will be reasonably hard, if you chose Treeko to start with. So, what should you do? Well, seeing as Absorb won't do much damage, and you can't level up to find an attack that will, I reccomend catching a Makuhita from the cave, back when you were about to battle Brawley. This way, you should have no troubles what-so-ever.
Gym Leader No.4, Flannery:
Now, Flannery uses the Fire type. So, firstly, here's the list:
Slugma: Fire type. Level 20
Camerupt: Fire/Ground types. Level 22
Torkoal: Fire type. Level 24
Numel: Fire/Ground types. Level 20
Alright, yet again, Marshtomp and Combusken are fine, and most importantly, Grovyle will have some trouble. So, this is almost a replica of the 3rd Gym.
When using Marshtomp, Water Gun and Mud Slap will come in very handy. Trust me, that's going to help heaps. And with Combusken, I reccomend just using either Double Kick, or Peck. Perhaps if you use Focus Energy, and boost your Critical Hit rate, then you might find things less challenging.
Now, the one thing for this is what to do with Grovyle. Now, you could use the Makuhita you used against Watson, but really, it's not going to do much damage. I reccomend you find and catch a Numel, then evolve it into a Camerupt. Once you do so, you can effectively use Magnitude against Flannery. Your only troubles will arise when Flannery's own Numel and Camerupt use Magnitude against you. Apart from that, you should be A-OK!
Gym Leader No.5, Norman:
Now, Norman uses the Normal type. So, firstly, here's the list:
Vigoroth: Normal type. Level 27
Slaking: Normal type. Level 31
Spinda: Normal type. Level 27
Linoone: Normal type. Level 29
Now, this Gym is so simple, you don't really need to do anything special. Combusken would be highly useful here, and you may get it to a Blaziken. Now, if you get wiped out when you are Grovyle or Marshtomp, you may consider using that Makuhita. By now, you'll find how useful little Mukahita can be. Really, that Gym should by fine.
Gym Leader No.6, Winona:
Now, Winona uses the Flying type. So, firstly, here's the list:
Swablu: Flying/Normal types. Level 29
Altaria: Flying/Dragon types. Level 33
Tropius: Flying/Grass types. Level 29
Pelipper: Flying/Water types. Level 30
Skarmory: Flying/Steel types. Level 31
Ouch, this Gym will be pretty hard. What you'll want would be a Swampert with Ice Beam. That will take care of most of the Pokémon. However, to take out Skarmory, you might need Camerupt, and for Pelliper, a Manectric could do well. So, the best team for a Swampert would have a Manectric with you.
Now, for Blaziken and Sceptile, you'll have to add in Manectric, and Camerupt. This will be the hardest Gym for you, and the second type of Winona's Pokémon vary. Really, you might need to battle her a few times. Eventually, you'll come out victorious.
Gym Leader No.7, Liza and Tate (Double Battle):
Now, Liza and Tate use the Psychic type. So, firstly, here's the list:
Xatu: Psychic/Flying types. Level 41
Lunatone: Psychic/Rock types. Level 42
Solrock: Psychic/Rock types. Level 42
Claydol: Psychic/Ground types. Level 41
Well, well, well. This is another one of those battles that are hard to get a grip on. Now, the first style is simple.
If you have a Swampert handy, this is going to be a walk in the park. Give it Surf and Ice Beam, and that's all four Pokémon down for the count. Even with Sceptile, you should be fine, just make sure you bring that Manectric, as you might need it against the Xatu.
However, thing's are a completely different story for you, if you have a Blaziken. Chances are, you might need a Pelliper, and use it the same was Swampert should be used. Surf and Ice Beam should take them down. However, if you don't have a Pelliper, bring Manectric for Xatu, and and hope for the best. Flamethrower, although not very effective, may make a bit of a difference against Lunatone and Solrock. And with Doulbe Kick, it will be a neutral hit against Lunatone and Solrock, so it could be useful aswell. And anyway, with persistence, you should get there.
Gym Leader No.8, Juan:
Now, Juan uses the Water type. So, firstly, here's the list:
Luvdisc: Water type. Level 41
Whiscash: Water/Ground types. Level 41
Sealeo: Water/Ice types. Level 43
Crawdaunt: Water/Dark types. Level 43
Milotic: Water type. Level 46
Alright, this battle will be easy. Now, for starter's, there are two way's to win in this battle. I'll outline them...
Okay, so, the first one is when you have a Sceptile. Now, if you had any sense, you would realise that all you have to do is use Leaf Blade. Now this move will absolutely destroy Juan. So really, on the lookout, there are no troubles.
Unfortunately, things won't be so easy with Blaziken or Swampert. Swampert will be easier to use, as really, all you need is to bring alone Manectric, and when it comes to the Whiscash, just swap in your Swampert, and you can Surf to victory. After you beat Whiscash, swap back to Manectric. Now, for Blaziken, you may have to take a risk. Manectric will be used as per usual, just when it comes to the Whiscash, you may have some problems. You may want to risk it, and try to use Sky Uppercut, or you could bring in my favourite Makuhita, who by now should be a Hariyama. So really, beat Whiscash, and you've won!
Hopefully, this guide has helped, and watch out for the Elite Four part of it!
Well, until then, Adios, Amigos!