This tutorial was written, so that players can modify their Generation 4 saves to perform cute charm abuse to obtain shinies.
Granted, it is possible for the user to legitimately reset their game to obtain an abusable save,
but the point of this guide is to allow users to make their own modifications to create such a save.
How it works
The ability Cute Charm in the overworld significantly increases the chances of the player encountering a Pokémon of the opposite gender.
In Generation 4, this is done by forcing the Personality ID of the opposing Pokémon to 1 out of 25 values,
that is preset and predetermined due to the Trainer ID and Secret ID.
As shininess is determined by Personality ID, Trainer ID and Secret ID, that means that certain Trainer ID and Secret ID combos,
together with Cute Charm, will generate shiny Pokémon.
This has been fixed in Generation 5 and onwards, and doesn't work for Generation 3.
Cute Charm only works on Pokémon that can be both genders, meaning it will not work on Pokémon that are 100% male ratio, 100% female ratio, or are genderless.
1. Ability to modify your save with PKHeX (save either dumped from cart, or snagged from emulator etc)
2. Ability to load back up and play with your modified save (send it back to cart, load save in emulator etc)
3. Have either RNGreporter or Pokefinder installed and working on your computer.
4. Ability to follow instructions, and a hella lot of patience.
1. Decide on whether you want your wild Pokémon to be male or female & what nature you would like.
Pick a PID from a table below that corresponds to your choice. (also remember what's gender lead is required)
The shiny Pokémon will you will encounter will be within the same shiny group.
For example, I want it to be female, but I don't care about the gender ratio of my intended opponent, and I would prefer a Timid creature,
so I chose 0000000A from the table above.
Image source: https://www.smogon.com/ingame/rng/dpphgss_rng_part5
3. Use your chosen PID to generate TID/SID combos. Choose the combination you favor.
For example, using the chosen PID of 0000000A, I generated multiple TID and SID combos, as per the image below.
In my examples, I've chosen 35880/35876.
4. Open PKHeX, and change your save's TID/SID.
For example, I edited my save based on my choice above.
5. Ensure that your party leads with the correct gender Pokémon and has Cute Charm.
For example, based on the Smogon Table above, I wanted to encounter Females,
The table states the lead I need is a Male (cause cute charm works on opposite genders).
I went ahead to ensure my 1st mon in my party is a male cute charmer.
6. Load back up the modified save, and encounter them shinies.
My trainer card showing that I changed my TID
My Shiny Encounters (within 10 battles)
For those that struggle with this
If you are struggling with the guide, and do not really care about the TID/SID pair you use, then you could consider using this:
Kazowar has a great video showing the effect.
Smogon has a great page regarding the abuse, as well as other RNG abuses.
Bulbapedia also as a page dedicated to the ability Cute Charm and it's specific mechanics.
If you are feeling lazy, I've got a page with some Cute Charmed Shinies I encountered. (I haven't been updating it, though).
If you need a save to modify (maybe for some reason, you don't want to use your own), I have all released generations saves here.