From the Super Mario Wiki
The Gooey Bomb is an explosive item that appears in the game Super Smash Bros. Brawl as a weapon.
It is mentioned that the Gooey Bomb is similar to the Motion-Sensor Bomb from Super Smash Bros. Melee, as, like the Motion Sensor Bomb, players can attach the Gooey Bomb to surrounding terrain; unlike the Motion-Sensor Bomb though, players can also attach the Gooey Bomb to opponents. The only way to remove a Gooey Bomb once it has been affixed to a character is to have that character run into another opponent, causing the Gooey Bomb to stick to them instead.
 Trophy Information from Super Smash Bros. Brawl