From the Super Mario Wiki
The Gooey Bomb is an explosive item that appears in Super Smash Bros. Brawl and Super Smash Bros. for Nintendo 3DS / Wii U 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. After a few seconds have passed, the Gooey Bomb blows up, dealing damage to the opponent it's stuck to and anyone in its vicinity.
Trophy Information from Super Smash Bros. Brawl