All or nothing coin

A Strange Silver Coin  2 inches across. One side glows slightly and has a angel holding a torch, the other side looks burned and has a horned devil in a cage . Inscribed in sylvan on both sides of the coin is " what's the most you've ever lost on a coin toss?". A creature can flip the coin to replace any roll that requires 1d20. When used they must roll 1d4; on a 1-2 the roll becomes a natural 1, on a 3-4 the roll becomes a natural 20. Once used by a creature, the coin falls on the floor and it can no longer be picked up or used by the creature that flipped it until they complete a long rest.