Hearthpwn

I quite liked your set. It has a lot of internal synergy, most card effects are simple yet interesting and most cards are balanced. Nice job overall. There are 3 things that could be improved, though:

1) The balance of a few cards.

The only card that is overpowered by itself is K'thir Cultist. This card is basically does a minor upgrade on Aldor Peacekeeper, which is a decent but not overpowered control card, which is perfectly fine. The problem is that Priest has too many ways to abuse low attack minions. This card + Cabal Shadow Priest is a Mind Control + healing + 2/2 + 4/5 on the board for 9 mana, which is a bit absurd against control decks. It is has quite a sick combo as well with Shadow Word: Pain, Potion of Madness and Shadow Madness. I think you could inscrease the mana cost and the stats accordingly, like to a 5 mana 3/4 with the same effect.

Another problematic card is Shadow Mend. It is quite interesting and perfectly fine by itself. However, combined with Auchenai Phantasm or Auchenai Soulpriest, it can do disgusting amounts of damage to the opponent's hero only for 1 mana, especially if Prophet Velen or Malygos are in play. In wild, this is even worse because of the existence of Embrace the Shadow, Flash Heal, Radiant Elemental, Shadow Visions and Emperor Thaurissan, which can further abuse this card. This card could be easily fixed by only being able to target minions and your own hero.

The only card I find underpowered is Mind Bender. I think it would be perfectly fine as a 3/4, but I undertand that you were conservative with this card given that it has the potential to snowball hard, specially with buffs.

2) The wording of some cards

Some of the cards have ambiguous or unclear effects. For example, it is unclear whether the healing of Shadow Mend comes immediately or along with the damage. It should read "Restore 3 health to a character and, at the start of your next turn, deal 3 damage to the same character." The other text that bothers me is that of Unassuming Frog. What is a faceless one? The card should at least tell the stats of the Faceless, and I think you should design a card for that token. I think a 5 mana 3/3 Faceless One would be fine balancewise.

3) The overcomplexity of the effects of the legendary minions

The legendaries were actually the cards I liked the most in your set. However, the effects were too complicated and could be simplified a little bit without losing its flavor. Azshara could read "Battlecry: Give all your opponent's minions: Deathrattle: Summon a 3/7 Naga to your opponent.". N'Zoth is harder to fix because, as you said, you have to adress Reno Jackson. I can't think of a better wording, but I think the text is a bit too long. Very cool effect though.