NHF – new heroes for Heroes V 3.1.

Personally, I don't want to. I just have a negative attitude towards such descriptions. Not everyone will want to spend their personal time just to find out how something actually works. But if an unknown surprise pops up in an important game (because the author didn't bother to describe it properly), that's definitely not good.

Is this a guessing game? People are different, their experience is different, and therefore different conclusions can be drawn from such descriptions.

What prevents accumulating fairies for ALL allied creatures? It says, "any creature." Isn't that for a reason?
Or accumulate and accumulate, and then, when a slot becomes available, dump a bunch of fairies for several days at once? This system worked in Heroes 4, if I remember correctly.