For a full explanation on this method, go to Smogon and search for the thread there. I will not post a link because it's probably against the rules.

This has been touched upon many times in this forum, but I don't think I ever recall a thread being dedicated to it. We have a thread about getting shinies through chaining, soft resetting, and the Masuda method, so here's a thread about the easiest and equally legitimate way, random number generator abuse. As a disclaimer, I am not an expert on this method, I'm just creating this thread because I feel that it's high time it was created.

First, since some of you may say RNG abuse is not legitemate, here is my short argument as to why it is. The random number generator, like EV's and IV's, is just a hidden value that Nintendo doesn't want us to know about. Sure they're hinted at in game, but to really EV and IV train requires us to use external sources to do things that could not be done with the game alone, while not changing the games code through a cheating device. The exact same is true with random number generator abuse.

Before I get into how exactly you do this, I will briefly explain what is going on. Any time a "random" event happens in the game, it calls a random number generator to decide its result. What this is is a very long string of integers, which it moves through sequentially. Where on the string it starts depends on what time you turn your game on according to the DS's internal clock. Luckily for us, Gamefreak decided to use the same string of integers as they used in Emerald, which is known by some extremely nice people who decided to make it public knowledge. Therefore, it is possible to calculate where on the random number generator you start, depending on what time you turn your game on and the IV's of the first pokemon you catch after turning on your game. From there, it's just a matter of advancing the RNG until it reaches the point where a shiny will be bred. Simple, right?

Before you start, you will need the following:
-Your SID (this can be found if you have caught one natural shiny, five chained shinies, or if you have an AR. Check Smogon for exactly how to find it)
-The coin flip app and the friend checker app on your Poketch
-Access to an area where you can catch level 50+ pokemon
-The RNG reporter

Once you have all of those, you can get started.

First, save your game in an area where you can catch pokemon of level 50 or higher. I save in the grassy area north of the Resort Area, and I use a level 50 pokemon first in my party while using a repel. This has worked for me every time. When you save, make sure you have a pokemon that knows fly, the two pokemon that you want to breed, and an open slot. The open slot is important. Also make sure your Poketch is not on the friend checker app. when you save.

Once you have saved, reset your game. When you continue your game, make note of the time (to the minute, not the second). To do this I just synchronized my computer clock to my DS clock. It's important that you get the time correct, or it will not work.

As soon as you start your game, walk around in the grass and catch the first pokemon you see. It should be level 50 or higher since you are using a repel. Since you had an open slot on your team, you'll be able to check the pokemon's stats right away.

In the RNG reporter, select "DPPt egg PID Normal" under the "Method" drop down, check the "Shiny only" check box, and enter your ID and SID. Once you have done that and you've done all of the previous steps, select "DPPt Seed Finder."

In the seed finder, select the "Find Initial Seed by Stats" option. You should have all of the information that is required for this, so input it. If everything is correct, then a seed should appear. Click on it, then hit OK. Once you are back at the RNG Reporter, click "Generate," and you should see a bunch of different pokemon options appear below.

Depending on what you want, you may have a preference on nature or gender or whatever. If what you want doesn't appear, reset and try again. If you see one you like, right click it and select "Calculate Poketch Taps." This will tell you how many times to double click the friend checker app (you will know you have done a successful double click if the pokemon jump up), and how many times to click the coin flip. Do the friend checker first. This is how you advance the RNG to where it needs to be.

Once you have done that, fly directly to Solaceon and put your pokemon in the daycare. If you've done everything correctly, the first egg the old man gives you will be a shiny pokemon.

Again, if you want a better explanation, go to Smogon. I am not an expert on this. If I have made any mistakes or if you have any comments, let me know.