Diamond, Pearl, and Platinum Egg RNG

Tools

PokeFinder
All tools needed for RNG abuse with Desmume
Access to the Daycare and information about your parents

Intro

This guide shows you how to advance the RNG to get the Pokémon you want. You should already know some basics about Gen 4 RNG, like how to start and advance it. Egg RNG in DPPt can be tricky due to background noise. The Masuda Method is an option but not required.

Setup

Getting ready is easy:

Open PokeFinder and go to Gen 4 => Eggs => Searcher.
Choose your profile and enter your parents' info. Parent A is the first Pokémon in the daycare, and Parent B is the second.
Drop off your parents at the daycare and save your game.

Hitting the PID using Egg Advances

Aim for an egg that doesn't need to advance the RNG, which is the easiest way:

In PokeFinder, set your Advance Range to 0-0.
Choose the specific traits you want for your Pokémon, like Shiny, Nature, Gender, Ability, etc.
Generate the results based on your criteria.
Select your target RNG advance.
RNG your Initial Seed.

If you need to advance the RNG beyond 0, bump up the egg advance before creating your egg. You can:

Use the Magikarp Coin to advance the RNG by 1.
Use the Happiness App (loaded or used) to advance the RNG 2 times the number of Pokémon on your team.
Reject the egg collection to advance the RNG by 1.

Don't forget to save your game in front of the old man.

Hitting the IVs

The second part of the RNG is more standard. Switch to the 'IVs' Method on PokeFinder and set your IV filters. Consider the IVs from your parents, and know that getting some 31 IVs is manageable. Get a result, hit your target advance, and advance the RNG like any other RNG. Be aware that timing the dialogue correctly is crucial due to some messiness in this area. Once done correctly, grab your egg, and you'll have your desired Pokémon.

Credits

Chinese translation: xuanyelin, Hakuhiro.