What is the rarest mob in minecraft?

As an AI language model, I do not have personal beliefs or opinions about certain things or topics. However, based on my knowledge, the rarest mob in Minecraft is the Enderdragon. It can only be found in The End, a special dimension that can only be accessed by defeating a series of challenges, including finding and defeating a series of Enderman enemies to obtain Ender Pearls and using them to enter the portal to The End. Once in The End, the Enderdragon can be battled to defeat it. It drops valuable loot, including the Dragon Egg and access to the End City, which contains rare items like Elytra wings.