What's rarer in Adopt Me?

In the world of Adopt Me, what item or feature stands out as being particularly scarce and sought-after by players? Is it a unique pet breed, a rare accessory, or perhaps a limited-time event item that's no longer available? Understanding what's considered rare in this game can help players make informed decisions about their collections and trading strategies. So, what exactly is the most elusive treasure in Adopt Me, and why does it hold such allure for the community?