I need help. 1) How do you get the shoal shells in the shoal cave and..

Shoal Cave
In the shoal cave you can get both the shoal shell and shoal salt, you just have to wait awhile and go wonder off. When you come back I'm sure the tides will be high and you'll have to use surf.

The Three Regis
Okay this is the hard part. You need both Relichant and Wailord.
To get Relichant you have to use dive around the Sootopolis area. Just go among the weeds and Relichant will pop out(sorry if I mispelled Relichant). Relichant pops out propebly a fraction of a 3 out of 10 so its pretty hard to find him. For Wailord use have to evolve a Wailmer. The best way to get Wailord the fastest is to use a super rod and try to find a level 32 Wailmer. After you caught Waimer just train him until level 40 and he'll evolve to Wailord or just use 8 rare candies on him so you don't have to train him. After having Relichant and Wailord go to Pacificlog town and surf to the left, but i warn you, you should always stay at the bottom. The tides will take you many different ways so its very very very very very hard to get to the exact same place where you want to be. If you go the correct way on the tides you should end up on a small area where you could dive down. After diving down, go straight until you see weird dots on the wall. Then dive up on the exact same place the dots are on. You will end up on a small room with a lot of stones with weird dots. Go to the last stone on the wall, you can see that it is much bigger that the other rocks, ask the wall and you will see a bunch of weird dots again, after done asking the back rock use dig. BAAAAAM the wall will open, go inside. There will be a room that looks exactly like the first but larger. As before go to the back of the room and ask the wall, there will again be weird dots. After asking it, carefully put Relichant in the first slot of all your pokemons and put Wailord at the last. Ask the wall again and there will be an earthquake.
Regiice
After the earthquake get out of the place and go to or fly to Dewford Town and surf up until you get to a small island with a lot of trees and a big fat guy wearing a blue shirt. Land on the island and surf left a little then up all the way until you get to a giant rock surrounded by littler rocks. There will be a door on the giant rock, go inside and as usual there will be weird dots at the back wall. Ask the wall and wait for 2 minutes(don't press any buttons after asking the wall just stay completely still). After somewhere around two minutes BAAAAM the wall will open right in front of you, go in and battle the legendary Regiice.

Registeel
After you beat or caught Regiice go to or fly to Lilycove City and go to the Route 120 and you should see some steps ahead of you go up and keep on going until you see the giant rock. Go inside and go ask the wall again at the back, when done asking it go to the middle of the room and use fly BAAAAM a door will appear, go inside and fight the lengendary Registeel.

Regirock
After Registeel comes the last Regi. To get this Regi fly to Mauville City and head up to the desert. When you get to the desert go right a little and then go down all the way till you reach the giant rock, go inside. Go ask the wall in the back, after that take 2 steps to the right then 2 steps down and then use strenght BAAAAM the door opens and here comes the final Regi.

Did you get the earthquake happen? If you did, Regice-Go to Dewford Town. Go to the side of Granite Cave. Surf up and left. You'll pass some islands.

Go up and see a cave? Thats Regice's! Go in and press A on the braille and wait for 2 minutes.

Go in and get Regice. RegiSteel-Go to lilycove and go left and go up stairs not in safari zone go up patch of grass go to cave go to middle and and use fly go in and get RegiSteel.

RegiRock-Go to desert and go right down go in cave braille says go right right down down use strength and get RegiRock.