NHF – new heroes for Heroes V 3.1.

Well, in this case, you can do it like with Sylvan's specialization (water element spells cannot be reflected).

You also can't do that with the water element. I'll repeat again: combat scripts are prohibited, meaning that what happens in battle is inaccessible to multiplayer (there is an option to hack the executable and figure everything out there, but that's only for masochists).

p.s. By the way, you can change hero parameters during battle, but you can't link anything to battle events, so it's useless.