This is one of Shulk's original arts when he starts out. It deals the most damage of his regular arts and has a bonus effect of dealing double damage if it hits from behind.
Super Smash Bros. series
In Super Smash Bros. for Nintendo 3DS/Wii U, this is Shulk's side special. When Shulk performs Back Slash, he lunges forward and slashes his opponent with his Monado as his Monado glows red. Back Slash does more damage and knockback when he hits his opponent from behind. Shulk cannot grab the ledge while performing Back Slash.
Back Slash Leap - greater vertical coverage at the cost of some horizontal distance and reach. It has less startup but, slightly more ending lag
Back Slash Charge - Shulk leaps forward with super armor. it has great horizontal distance but much less damage and knockback if it doesn't hit in the back