Which egg gives Shadow Dragon in Adopt Me?

Excuse me, could you clarify for me which specific egg in the Adopt Me game has the potential to hatch a Shadow Dragon? I'm a bit of a novice when it comes to the finer details of the game's mechanics and I'm eager to expand my collection of rare pets. Could you possibly elaborate on the rarity of this particular egg and any other details that might be helpful in my quest to obtain a Shadow Dragon?