Wondrous item, rare
A coin of a random metal type, though usually gold or platinum. It appears like any other coin, usually in a purse or other collection of coins, but frequently at the site of an unlikely disaster that killed its prior owner
Curse. Once this coin comes into your possession, you experience incredible bad luck. Whenever you roll a d20, the DM also rolls a d20 and you take the lower of the two (or three if you have advantage or disadvantage). Results of 1 or 2 on any check result in embarrassing mishaps that escalate until the around the 20th the mishaps start to become potentially deadly.
The curse can only be removed by containing the coin in a lead box, death, or transferred by using the coin unknowingly in a purchase.
The unlucky coin from Odd Squad inspired this item. I imagine it being found in the remains a wagon crushed by a fallen boulder.