The effect is created by Adrian Mendez.
Take a look at this awesome red slash effect made by VFX Artist Adrian Mendez in Unity. Additionally, the artist used Substance 3D Designer, Houdini, EmberGen, and After Effects to get the fantastic visuals to work just right.
Mendez has been on 80 Level before, with his impressive shader-based freeze gun.
Here are some other works from the artist: