How do you get Regice in Pokemon Emerald?

Okay, first of all you need a Wailord (Lv. 40 evolution of Wailmer), and a Relicanth. Relicanth can be found underwater in the grass around the cave where Sootopolis City is. This will take a while, but i guarantee you will find one. Wailmer can be found either by surfing or, usually, by fishing. When you fish, use a Good Rod or a Super Rod. Trust me, it works. Also, make sure one of your Pokemon knows "Dig, Surf, and Dive." After you're all set with that, go to Pacifidilog Town. Go ALL the way to the left and surf. Stick to near the bottom until you pass two islands. The third one is tricky. You go to about the middle on the right side. Now, surf again. You SHOULD end up at a dark spot where you can use "Dive." If done incorrectly, you will end up in Slateport City. Go under water and head down. Go up when you see the braille (The dots on a big rock). You have entered the Seafloor Cavern. Now keep walking forward until you come to the other side. There should be more braille(the dots). Now you use "Dig" and the door will open to the next room. Go all the way to the other side again and the braille will actually read, "FIRST COMES WAILORD LAST COMES RELICANTH." Now this is very simple. Put Wailord first in your party and Relicanth last. The next door should open up. Now three new caves have appeared all over Hoenn where Registeel, Regirock, and Regice are now. Registeel is on Route 120 in the Ancient, Regirock is on Route 111 in the Desert Ruins, and Regice is on Route 105 in the Island Cave.

To get Regice, go to Dewford town then surf like you are going to petlburg until you see the small island. Go on the island. It divides up the water. Go to the left side and surf up. You will enter the cave. Go read the sign. Then starting from left, walk all around the cave's edges and only the edges. Then it will open. There will be a level 40 Regice. It's moves are curse, superpower, ice wind and charge-beam or ancient power. The last 2 moves depends on what level your wailord and relicanth are. Keep on using ultra balls. Have over 25 ultra balls, 15 great balls and 15 timer balls. Only use the timer balls after it has been 20 turns or more. Do not give it a nickname because if you want to migrate to pearl or diamond you must have regice, regirock and registeel, if your going to get reggigigas. They have to have there original names or they will not be considered regirock, regice or registeel.

To get registeel in emerald, go to the center of the cave and use flash and the second cave to open registeel. To get regirock, go straight to the middle of the of the braille wall click on it and then go left, left, down, down, and then use rock-smash and the second cave to regirock will open. (Do not do the same for ruby and sapphire they are different.) and for regice sometimes u need to go around twice but on the inside of the cave.

You can find it only once in the Island Cave, in Route 105. Hope I helped :)Okay this is gonna take a while. Go to the bottom bridge parts of Pacifidlog Town and continue left. Then follow the currents to a fisherman. Then go north and use surf and continue left but go on the left side other wise you have to start over. now then you reach a calm spot so now go south under the rocks and continue south to the currents. (Remember don't go on the 2nd way down Go on the first way down) So then cross it and you'll end up on a small white path of land go two down then continue west to get to the calm spot. Then go underwater and go through the opening to the underwater surface then go south and look at the writing and use dive. now go north and read the Braille (I can read Braille and it says Dig here) So remember to dig here by getting dig from the fossil maniac's house. Now go north then the 3 cave doors won't open unless you have the Pokemon Relicanth which can be rarely found near sootopolis underwater and Wailmer which can be found in the ocean with a super rod. Put Relicanth first in line and then put Wailord (evolve Wailmer) last in line, an earthquake will happen and the doors will open.
Assuming you've already unlocked it, just try to capture it as you would any other Pokemon. I recommend freezing, paralyzing, or putting Regice to sleep. Make Regice's HP as low as possible and start throwing Ultra Balls at it.