A longheld Pokemon fan theory was debunked thanks to an article recently translated into English. Munna is a Psychic-type Pokemon that looks like a pink tapir that floats in the airs. Munna has the unique ability to eat the dreams of other Pokemon and can then project the dream using Dream Mist, a vapor-like substance that it expels from its nose. While the Pokemon wasn't introduced until Pokemon Black & White, many fans believe that it's actually much older, thanks to a throwaway comment made in Pokemon Red & Blue. In the original Pokemon games, a Trainer NPC on Route 10 mentions wanting to see a "chunky Pokemon" that's pink and has a floral pattern, which matches Munna's description almost exactly.
However, a 2011 interview of Ken Sugimori recently translated into English by the YouTuber Dr. Lava debunks this theory entirely. The interview originally ran in the Japanese magazine Nintendo Dream and detailed the designs of various Gen V Pokemon. When discussing Munna, Sugimori noted it was designed by Atsuko Nishida, the person responsible for designing several popular Pokemon, including Pikachu. Nishida had no requirements when designing Munna, and she returned with a design for Mushara, Munna's evolved form. The Pokemon design team decided to make Mushara a two-stage Pokemon, so they then designed Munna afterwards.
The interview also mentions several instances where scrapped Pokemon designs were re-worked to become Gen V Pokemon, and it doesn't appear that this was the case with Munna, since it was designed after Nishida submitted Mushara to the Pokemon design team. And while it's possible that the design team drew some inspiration from older games (especially as the dialogue re-appears in both Pokemon Gold and Silver and Pokemon HeartGold and SoulSilver, Sugimori doesn't mention that at all, which seems suspect given that he goes into remarkable detail about how Pokemon were designed in the interview.
You can find the full translated article here, which contains tons of information about some "Gen V" Pokemon and some Pokemon that didn't make the cut.