Slingsniper is Luigi's fourth available Bros. Attack in Mario & Luigi: Dream Team. Like the 3D Green Shell, this Bros. Attack is mandatory to obtain as the Attack Pieces for it are given to Luigi by Big Massif and Lil' Massif after completing the Ball Hop puzzle on Mount Pajamaja. 9 BP is required to use this attack.
When the attack is initiated, a large slingshot is planted in the foreground of the battlefield. Once Luigi climbs inside the slingshot, the player will have to hold down on the Circle Pad to allow Mario to stretch it further into the foreground. Once the slingshot is fully stretched out, the player will have to hold down the 
button while tilting the 3DS to aim the slingshot. Letting go of the button will automatically launch Luigi in the direction the aiming reticle was pointing. The attack will fail if the player takes too long to aim or if Luigi misses the enemies. If the player lets go of the Circle Pad before pressing the button to fire Luigi, it will automatically fire and will deal a minimal amount of damage to a random enemy. It is possible to hit several enemies in a row with the attack.
The Slingsniper does critical damage to Pi'illodactyls, Wiggler, Pi'illodactyl Rs, Pi'illodium, Grobot X, Torkscrew X, Mammoshka X, Dreamy Bowser and Pi'illodium X if it strikes them where a star mark appears, presumably indicating their weak spot.
Description
Slide and hold the Circle Pad down to draw back, hold the B button, and aim. Tilt the 3DS to line up your target, then release the B button to launch Luigi!