Peach Bomber is Princess Peach's Side B move. She lunges her rear end towards her opponents and blasts them with a powerful explosion.
Using the Peach Bomber on most walls in the game will cause Peach to rise upward a tad. This can help with recovery on stages with vertical walls, such as Yoshi's Story and Fourside. The technique can also be used to stall a match, as Peach can continue to bomb the walls, keeping her alive and out of range for most other characters who would be KO'd if they were to try to go and attack her. Use of the technique in this way is banned in most tournaments.
In Super Smash Bros. Brawl, it has been altered visually to have a heart shaped explosion when the attack connects. When used it also covers more distance than in Melee. Also, it now can't be used to bomb normal walls for vertical height gain. However, if a wall is destructible, such as those in Shadow Moses Island, Peach can still rise a tad upward.