A hidden feature in these Pokémon games is the ability to tell a certain NPC four specific words or phrases using the easy chat system in order to unlock special rewards. Which words are required are unique per save file.
In Diamond, Pearl, and Platinum these rewards include 8 different special PC box wallpapers. The NPC to speak to is located on the 3rd floor of the Jubilife TV station.
In HeartGold and SoulSilver, rewards include 8 different PC box wallpapers plus 3 different Pokémon eggs. The NPC to speak to is located in the Violet City Pokémon Center.

The original distribution of these passwords was via the Pokémon Daisuki Club, a defunct, Japanese-exclusive official fan club website.
Below is both a calculator to generate the passwords for your specific save file, an in-depth explanation of how the password check system functions, and a full dump of the relevant word data.
Everyone groans. The flaming pumpkin finally sets off the smoke alarm. Lily serves the subpoena. Fade to black on a title card:
"Lily, sweetie, we talked about this. Halloween is about fun threats, not real ones."
: The one that started it all. Claire attempts to stage a massive haunted house, but her plans are derailed by Mitchell’s office costume mishap (dressing as Spider-Man for a non-costume office) and Cameron's deep-seated trauma regarding the holiday. modern family halloween
The whole family gathers at the Dunphy house for the annual "Best Costume" vote. Gloria wins (as always) because she looks like a supermodel in fangs. Jay is eating candy corn directly from the bowl, grimacing. Phil’s QR code costume accidentally scans and starts playing a Nicki Minaj song at full volume.
If there is a reigning Queen of Halloween in the Dunphy household, it is undoubtedly Claire. For her, Halloween wasn't just a holiday; it was a project management exercise with a deadline. Everyone groans
Jay and Gloria’s house. It is eerily quiet. A single, elegant skeleton made of real Italian marble sits on the porch. A bowl of organic, gluten-free candy corn sits next to it.
From the Dunphy house to the Pritchett-Tucker residence, each household brought its own unique flavor to the holiday. Fade to black on a title card: "Lily,
Jay Pritchett served as the Halloween curmudgeon, the man who didn't see the point in buying a six-foot spider for the front porch. Yet, the show always found a way to weaponize his skepticism for humor.