Within the data for Pokémon Diamond, Pearl, and Platinum is code to spawn in a Level 40 Darkrai as a roaming Pokémon, tying in with its nature as a malevolent counterpart to Cresselia (which similarly becomes a roaming Pokémon after meeting the player on Fullmoon Island). In the final game, Darkrai is instead encountered as a stationary opponent at Newmoon Island after obtaining the Member Card as a Mystery Gift item at select in-person events.

On March 21st, 2009, the Nintendo World store in New York City held a Pokémon Platinum Launch Event to celebrate the game's release. However, flyers were distributed around Nintendo World stating that attendees can receive a Mystery Gift, which turned out to be a hacked shiny Gengar caught in a Safari Ball, with its nickname being a racial slur used against black people. Its moves were based on black stereotypes consisting of Thief, Sucker Punch, Sludge Bomb, and Snatch along with the Truant ability. The flyers that were distributed around Nintendo World turned out to be a Photoshop edit of the original flyer that didn't specify any Mystery Gift being given out to attendees at all. The Photoshopped flyers were intended for an unrelated unofficial distribution of an Eevee that was also occurring at Nintendo World. The people distributing the Eevee quickly stopped their distribution when security questioned them about the racist shiny Gengar, as two wi-fi signals were detected at Nintendo World. Reports have speculated that an overweight African-American man dressed as a common Team Rocket grunt was solely responsible for the hacked shiny Gengar distribution, and that he was later arrested by police. Nintendo issued an apology regarding the controversy stating that anyone should refrain from downloading the hacked Mystery Gift Pokémon to avoid any data corruption.

Like Pokémon Diamond & Pearl, Pokémon Platinum contains the unused Azure Flute item, which triggers a battle with a level 80 Arceus in the otherwise inaccessible Hall of Origin atop Spear Pillar. The event is almost identical to how it appears in Diamond & Pearl, with the sole difference being a redesigned sprite for Arceus. The Azure Flute was intended to be given out to players as an event item, but was scrapped due to concerns that it would be too confusing for players. Instead, Arceus was directly given out as an event Pokémon.

The music for the Hall of Origin and the battle against Arceus, which are carried over from Diamond and Pearl, go unused here too, but the latter song would be reused for the Sinjoh Ruins event in Pokémon Heart Gold & Soul Silver, where players can obtain a Dialga, Palkia, or Giratina if they have an Arceus at the front of their party. This event additionally contains code allowing it to be triggered by an Arceus from the Hall of Origin, indicating that Game Freak still considered distributing the Azure Flute this late into Generation IV. Spoiler:The Azure Flute and Hall of Origin would eventually be implemented in Pokémon Brilliant Diamond & Shining Pearl, where players can access both if they import Pokémon Legends: Arceus save data after catching Arceus there.

In Platinum and HeartGold & SoulSilver, Bidoof's gender difference has more to it than in any other game. In Diamond & Pearl and every future game after HG/SS, Bidoof's gender difference is that the male has an additional 2 curls on the tail. However in these 3 games, Bidoof's patch of white around the face has a more pronounced bump in between the eyes on the male, with a more flattened bump on the female. Whether this is intentional or not is unknown, but due to the fact it was fixed later in Generation V, it's safe to assume this was a mistake.

The character Looker bares a strong resemblance to Koichi Zenigata, a fictional detective in Monkey Punch's manga series, Lupin the Third. This is most likely intentional since Lupin the Third was released when many of the Game Freak developers were young.

Lilycove City's theme (from Ruby and Sapphire) can be found in Pokemon Platinum. It is played on the Audio System that can be obtained at the Villa in the Resort Area.

The European versions of the game have 'Game Machines' rather than slot machines. As playing slot machines is needed to obtain TM64, the European versions of Platinum will occasionally reward the player with the TM while talking to the Game Corner's receptionist. The reason for this change comes from implementation of more aggressive and strict legislation in the European Union towards gambling.

In the non-English European versions of Pokémon Diamond and Pearl, Registeel's sprite was changed because the position of its left arm was similar to the Nazi salute. In Pokémon Platinum, the sprite was changed for all regions to the continental European variation. This change was retained in HeartGold and SoulSilver.

"Looker", a character who hides his real name, says that he is working to stop Team Galactic from ripping reality into pieces and creating a new world to replace our own. He wears a brown coat and a suit, and has very pointy hair. He seems very similar to "The Doctor" from "Doctor Who", who also goes around stopping galactic cataclysmic events, and never reveals his actual name. In addition, "Looker" physically resembles the tenth Doctor portrayed by David Tennant.