These are pure collictible pieces :)
A collectible card has no race and rarity. It cannot be got as a reward, cannot be crafted or upgraded. It is not shown in the library. A player can only summon it occasionally.
One more thing - the player can have only one collectible card of the same type in the deck. Here is the teasing picture of the first card.
PS: There will be an achievement for collecting such cards in the game ;)