Hi 
The “secret” of the projectile is a sine-shaped texture and a trail which is thin at the start and then quickly scales to it’s defined width. The principle is basically the same like here for the angel wings: sine texture on a plane where one part is scaled down → nice wiggly motion (Diablo 3 – Wings of Angels | Simon schreibt.)
In addition the trail uses UV distortion BUT
- only for the vertical UVs (meaning only for V, not for U)
- The distortion intensity gets stronger over time (so at the start of the trail there is no uv distortion and at the end of the trail it’s full intensity). This makes the trail move the “older” the ribbon particles get.