It comes in the form of a d-20 dice. You first clearly state out loud what you want to happen then roll it. If it lands on a 20, then what you want will exactly happen. If it lands on a 10, nothing happens. If it lands on a 1, the exact opposite of what you requested will happen. Landing on 11-19 will cause what you want to happen via varying degrees and landing on a 2-9 will cause what you don't want to happen via varying degrees, both depending on how high or low the number is.
For example:
If I want 1 mil dollars and I roll a 20, I get a mil dollars. If I roll a 1, I am 1 mil in debt. Landing a 5 means 500k debt, landing a 10 means I don't gain or lose money, and landing a 15 means I gain 500k.