The most exciting thing about this legendary Priest alt-hero isn't its Battlecry ability, but the new hero power that turns into Voidform (Deal 2 damage. After you play a card, refresh this.)
Priest has tons of zero- and one-mana cost spells that can be used to refresh the new hero power. And with the help of Raza the Chained, the hero power itself will cost zero as well. This potentially allows Shadowreaper Anduin to perform a one-turn kill (OTK) before turn 10.