I'm on this same part, it's pretty complicated. First thing is first; try and level up.
Get to Level 48 at the LEAST. That will give you a nice boost with power, 50 if you want
a
bit more of an advantage. Next you're going to want to get some Reviver Seeds, make sure
you get a lot; 10 or more will do fine.
Items You May Want:
Reviver Seeds - Quantity: 10-20
Oran Berries - Quantity: 10-15
Sleep Seeds - Quantity: 5-10
X-Eye Seeds - Quantity: 5-10
( Any Seeds that may cause confusion, posion, or paralysis ) - Quantity: 5-10
Iron Thorn - Quantity: 5-10
Stick - Quantity: 5-10
After you get to the part where you have to fight the guild go as following:
1-You want to take out Diglett and Dugtrio first. Dugtrio can use 'Earthquake', which has
100Power and 100Accuracy. But on the bright side, it hits everyone. Diglett has 'Earth
Power' which is just as strong with 90Power and 100Accuracy.
2-Next, if you have a Pokemon with the move 'Sleep' or 'Yawn' use it on Wigglytuff, his
'DoubleSlap' is pretty strong. If you don't have the move 'Sleep' or 'Yawn' use a 'Sleep
Seed' or something that will keep him out of the way. Make sure to keep him like this
till
the end.
3-Sunflora is easy to beat, use a couple of Tackles and a strong attack and she's out.
4-After you have Diglett, Dugtrio, and Sunflora out, and maybe a couple more depending on
the status of your partner; try and get Chatot. He knows the move 'Hyper Voice', which
has
90Power and 100Accuracy.
5-After you beat Chatot, beat any other guild members you may have still living, after
you
beat them go to step 6. (DO NOT TAKE OUT WIGGLYTUFF)
6-During all this make sure you keep on having Wigglytuff out of the way, whether he's
sleeping or paralyzed. He will be the last Pokemon you beat, make him paralyzed or
sleeping and restore your health. Then Attack! Use your most powerful moves to win. If
you've run out of PP use a 'Max Elixir' these things are extremely helpful!
After you beat the guild continue on to "Luminous Spring".
Guild Members Weaknesses:
Wigglytuff- Fighting Types
Chatot- Electric/Ice/Rock Types
Croagunk- Ground/Flying/Psychic* Types
Loudred- Fighting Types
Chimecho- Bug/Ghost/Dark Types
Sunflora- Fire/Ice/Poison/Flying/Bug Types
Krabby- Electric/Grass Types
Diglett- Water/Grass/Ice Types
Dugtrio- Water/Grass/Ice Types
Hope I helped!