The X Bomb is a new item introduced in Kid Icarus: Uprising. It explodes shortly after being thrown, releasing 4 large quick and strong projectiles that spread out in an X-shaped fashion, hence the name, which is also to pierce through multiple enemies. The projectiles themselves can even change directions if it hits a wall, making the X Bomb excellent in narrow areas. The directions of which the X Bomb explodes depends on the direction it's facing once it hits the ground.
X Bombs explode shortly after being thrown, ripping through multiple enemies for massive damage with their cross-shaped blast. The orientation of the explosion depends on the direction faced when the bomb is thrown.
In Super Smash Bros. 4
The X Bomb appears as an item in the upcoming Super Smash Bros. for Nintendo 3DS/Wii U. It releases an explosion in the shape of a cross. While the item originates from Kid Icarus: Uprising, its explosion is actually based on the X Bomb item that appears in the Meteos series.