Hearthpwn

Hmmm anyone knows if the stored card is a copy or not? 

It is not a copy, it draws the card from your deck, thinning it out.

Priest can copy this card for your entire board and Shard of Naru / Mass Dispell to destroy your deck. There will be a YouTube video on this, I can't wait.

Priest isn't known to fill your opponent's board with copies of a minion

What do you mean?

It has the stats of a 2 mana card to eventually draw you 1 or more cards.  It's slow to get its payoff, and has the potential to seriously backfire if the opponent instead lets it sit and accumulate too many cards.  But there's also some weird combos you can do by triggering its deathrattle multiple times to duplicate cards, even potentially infinite cards if it banks a Play Dead or some such.

I truly hope it shows you which cards it is banking when it does so, allowing opponents insight into whether they want to silence it or not to send the banked cards into the void.