Light-G

From the Super Mario Wiki

Light-G is a status effect in Mario & Luigi: Superstar Saga. It stands for "Light-Gravity". Mario and Luigi are the only ones who can be afflicted with this status. The brothers can get this status by wearing certain Clothing, or by eating a Green Pepper.

As its name suggests, Light-G will cause the Mario brother to become lighter, meaning his jumps will descend slower, and his Hammer attack will be faster. It is indicated by feathers floating up from below Mario or Luigi.