David-S Old School Version. Arinix is the deity of luck and fortune in my campaign world.
Arinix's Coin
This magical silver coin bears the face of Arinix, God of Fortune, on both sides. One face smiles broadly, while the other scowls. If it lands on the scowling face, the reversal of fortune is triggered.
Reversal of Fortune: Once per day, the bearer may toss the coin into the air and invoke Arinix's name. For 1 turn (10 rounds), fortune is reversed in a 100-foot radius around the coin.
For the duration, all bonuses to attack rolls and saving throws become penalties, and all penalties become bonuses. For example, a creature that would normally receive +2 to an attack roll instead suffers –2. A creature suffering –3 to a roll instead receives +3. The effect applies to all creatures and effects within the area, including the bearer. Bonuses or penalties that arise after the coin is activated are also reversed.
The bearer may end the effect at any time by picking up the coin. It can be used once every 24 hours.
Rumour: It is said that Arinix created the coins after a mortal gambler complained that fortune was never fair. Arinix agreed, and made certain that, for a brief time, bad luck was every bit as powerful as good luck.