The Bonus Ring is an item that appears in Mario & Luigi: Superstar Saga. It can only be obtained by making espresso at Starbeans Café for the second time. Professor E. Gadd will appear and hand over this accessory to Mario and Luigi.
The Bonus Ring is a pentagon-shaped ring that is gold in color.
When equipped, the Bonus Ring doubles the amount of Experience Points won at the end of battles. This can be very useful to level up quicker and should be equipped against bosses and a horde of enemies.