From the Super Mario Wiki
in Super Smash Bros. Brawl
Sandbag is a living punching bag in the Super Smash Bros. series. First appearing in Super Smash Bros. Melee, it is the target in the Home-Run Contest.
Sandbag also makes three appearances in Super Smash Bros. Brawl. In the Wi-Fi connection mode, as players are waiting for the game to load, or other players to connect, they are able to attack Sandbag on the waiting screen. It will also appear in the Home-Run Contest mode of the game, once again. It also appears as a container, but can "lose" several items unlike other containers. A very common cheat is to use Sandbag only, which makes it constantly drop Stickers and CDs.
In Super Smash Bros. for Nintendo 3DS / Wii U, aside from appearing in the Home-Run Contest, it also is introduced as a regular item during fighting matches.
Super Smash Bros. Melee Trophy
||Sandbag exists for one reason only: to get smashed in the Home-Run Contest. Pound on Sandbag as much as possible in the time allotted, then swing for the fences as you compete for the longest home run of all time. Getting hit doesn't hurt Sandbag at all. As a matter of fact, it loves to see players wind up and let loose.
Super Smash Bros. Brawl Trophy
|| GCN Super Smash Bros. Melee
|| An item that appears in the Home-Run Contest, where the goal is to do lots of damage to Sandbag, then send it flying as far as you can. It also appears in the regular game. If you smash it, a storm of confetti and items will burst out. Sandbag doesn't feel pain, though; in fact, it's happy to be of service.
| Wii Super Smash Bros. Brawl
Names in other languages
||Sac de Sable