Indepth Horde Shiny Hunting Guide

I found this awesome tutorial and thought to share.

OVERVIEW

The fundamental idea behind Horde Shiny Hunting is that, assuming that the Pokémon generation algorithm is the same for each member of a horde as it is for a single battle, a horde gives you five chances to encounter a shiny in roughly the same amount of time as a single encounter, making the process go by much more quickly. (In addition, it can be very thrilling to see five identical silhouettes and have one of them be in a totally different color scheme.)

The most practical way of summoning a horde is to use the move Sweet Scent, which can be learned by a number of Pokémon (Combee and Oddish are notably common; I use a Tropius because it can also Fly me around Kalos to access different routes). Using Honey from your inventory has the same effect, as well, with the downside of being in finite quantities. If the route or cave can have hordes appear on it and it isn't raining (which dissipates Sweet Scent), a horde will appear.

PROS AND CONS

Pros:
It goes by more quickly, and it's possible to have some degree of control over natures (using Synchronizers in the lead position) and gender distribution (using Cute Charmers in the lead position), and there's a small chance of the Shiny having its Hidden Ability.

Cons:
You have no control over IVs, and there are a very limited number of species available. In addition, you can only catch a horde member once every other member of the horde has been knocked out, which carries its own pitfalls (more on those below).

CATCHING YOUR SHINY

Once you've encountered a shiny, the obvious course of action is to KO all of the other Pokémon in the horde, one way or another, before (optionally weakening the shiny and) throwing Poké Balls. Obviously, then, you should have Pokémon in your party that are strong enough to KO the non-shinies quickly and/or make the shiny easier to catch once you've eliminated its compatriots.

STATING THE OBVIOUS

Stock up on Poké Balls and, if necessarily, PP-restoring berries, because you never know when a battle might drag on. Roggenrola hordes in particular love to spam Sand-Attack, so a guaranteed-hit attack like Magical Leaf may not go amiss.

Know what you're looking for. Knowing what the shiny sprites of the Pokémon you're encountering look like (or at least knowing how they differ from the regular sprites) can alleviate a lot of paranoia regarding whether or not a shiny is present if you're not paying attention.

Pay attention! Horde Pokémon are arranged left to right, and they correspond with the targeting names from the bottom left to the bottom right, going clockwise. Know which Pokémon you're trying to hit and what attack you're trying to hit it with. There's nothing quite so tragic as watching a Magical Leaf connect with the wrong target or accidentally hitting Surf when you meant to hit Aqua Jet.

PROBLEMS AND SOLUTIONS

There are a number of horde battles that have various idiosyncrasies that make capturing a shiny member more difficult. Namely, these are:

Durant/Heatmor and Zangoose/Seviper: Spawning in four of one species and one of the other (depending on version), the two disparate species will fight each other before fighting you. If you're shiny hunting on a route with one of these two types of hordes, you'll want to have some way of preventing any shinies from being killed. Some ways to do this are:

Use Darkrai's Dark Void (if you have it...for some reason?) to put all members to sleep and KO the non-shinies at your leisure

Use Growl (an area-of-effect attack) to declaw the entire horde while you KO the non-shinies

Use Heal Pulse to heal the shiny whenever it gets low on HP

My personal favorite, Skill Swap Levitate on to the Shiny (the Chimecho line is the most practical Pokémon for this, although some other PokéBank-only Pokémon can also do it) and use a ground attack like Earthquake to KO everyone else.

Use Trick-Or-Treat (signature move of the Gourgeist line) to add the Ghost-type to a shiny, then use an all-enemies Normal-type move such as Explosion or Swift

Me First can be used to force all horde members to attack your Pokémon instead of each other.
Geodude and Graveler Hordes: These hordes have a similar problem to the above, in that the members tend to indiscriminately Magnitude each other to death. Again, you'll want to be able to keep any shinies you encounter in these hordes alive somehow.

Trick/Switcheroo an Air Balloon (available at the Battle Maison in Kiloude City for BP) onto the Shiny and let the non-shinies Magnitude the life out of each other. This is more practical here than in the hordes above because the horde Pokémon won't attack each other and pop the balloon prematurely. And if you successfully catch the shiny, you get the Air Balloon right back!

As with the above, Skill Swapping Levitate also works here, as does using Telekinesis to make the shiny Geodude/Graveler immune to Magnitude.

If you have a fast-enough Smeargle and are feeling particularly clever, you can teach Smeargle Magnitude and Imprison. Using Imprison in a horde battle will lock out Magnitude on all opponents, making sure that they attack you with single-target attacks only.

Unhelpful Camera Angles: You'll notice over a large number of horde encounters that the camera angle often changes from horde battle to horde battle. This makes it particularly important to have your audio on, or at least by acutely aware of what the shiny versions of the Pokémon you're encountering look like, for the following reason: there is no guarantee that the shiny will be visible on screen when its sparkling effect occurs. I found this out tonight from experience -- if you don't have your audio on to hear the characteristic sparkling sound, you get a close camera angle, AND you encounter a horde species with little difference between its normal and shiny sprite (Plusle, I'm looking at you), you would have no way of knowing that a shiny is there. (Luckily for me, Shiny Psyduck was ridiculously obvious.)

CONCLUSION

I think that covers everything I had to say about hunting for shinies in hordes...if anyone has more advice to add, by all means please post it! Happy Hunting!

Source: [here]