The muzzle flash shown is NOT part of the spell. It was a mod that failed to be removed, promos will be updated to not include that in the future.

This spells works on the following weapons:

Rocket Launchers
Stickybomb Launchers
Grenade Launchers
Sentry Gun Rockets
The Caber

The size, duration, and opaqueness are based on the existing in-game spell, Pumpkin Bombs.