What is the rarest thing to find in Sea of Thieves?

Ahoy there, matey! I've been sailing the high seas of Sea of Thieves for quite some time now, and I've got to ask - what's the rarest treasure to be found in those treacherous waters? Is it a chest filled with doubloons that could make even the most seasoned pirate's heart skip a beat? Or perhaps it's a cursed artifact that holds the power to sway the tides in your favor? Whatever it may be, I'm itching to know the answer! So, what say you, fellow pirate? What's the rarest thing to find in Sea of Thieves?