Effect updates and description can be seen here.
This spell card was added in Beta 3.7, along with the Sans rework. The only monsters who can make this is Sans, and Gaster. This is one of the ways Sans and Gaster can attack, both only having 1 ATK (while Gaster can't even attack at all). This can deal 8 damage to an monster, which can most likely kill that monster, or deal 5 damage to the enemy player. That would deal 1/6 damage of the enemy player's health, unless they're DT.