"Special attack" is a new one introduced with her. As such, I don't know are there proper posts about it, but to my understanding, it's yet another modifier which means that it's extremely potent.

Simplified damage formula with after this would be Assault*Elemental*Berserk*Special, which means that you can do crazy numbers. In theory. The downside is, your Assault % will be garbage due to using multiple elements.