In short, there was a leak or something like that. In general, brief dossiers on 3 already known races became available, of course, in English. In particular, their racial abilities were briefly revealed. I will quote HugoLock:
* For humans - Guardian Angel: a friendly unit becomes immune to attacks and negative effects (presumably for a limited time).
* For demons - Gating: works similarly to the "opening of gates" from Heroes V.
* For Necromancers, the traditional Necromancy has been preserved, but it now works differently: creatures that fall in battle now accumulate a certain "counter," which can be used to increase the number of one of the Necromancer units directly in battle. After the battle, only a portion of the raised undead creatures remains.
You can find more details at this link. You can also find some new artwork there.
I haven't read the PDFs myself yet; maybe I'll translate some facts and post them today or tomorrow.