* "Unknown" Pokemon: HeartGold has a few Pokemon not found in the original Gold and Silver games. These include:
* Jirachi: Found by using the "Wish" feature in a specific location.
* Deoxys: Found through a special event.
* Darkrai: Found through a special event.
* Shaymin: Found through a special event.
* Secret Bases: HeartGold lets you build and customize your own "Secret Base". You can find other player's bases and leave messages, trade items, and more.
* The "Unknown" Pokémon: This is a term used in the anime, and it is believed to be based on the "Ghost Pokémon", Gengar.
If you can provide more context about where you saw this "unknown project," I might be able to help you find the answer!