Next: a 3-mana 3/6 that has an unique  drawback that no existing Hearthstone card has.

So sure you can play him for 4 mana and get 4/4 minion which is okay, but if you somehow manage to reduce  his cost to an odd number, you get a Boulderfist Ogre for less mana. Combo with: Sorcerer's Apprentice, Pint-Sized Summoner, Preparation, Shadowfiend, Far Sight, Emperor Thaurissan and Wilfred Fizzlebang.

At first it seems OP I mean this worth 7-6 mana atleast, you get it for 4 mana. But the catch is the health lose, the more this minion lives, the more health you lose, you can't even use your hero power because you are gonna lose 5 health atleast. So the whole point that this minion is really hard to remove (4 attack = immune to both shadow words) and very sticky (8 health), but the more he lives, the more health you will lose, is it good or bad? You decide. Kinda interesting concept, playable? I don't know but certainly interesting and better than the original.

Next: Blood Imp

I really like some of the ideas for your cards, but alot of them are or unbalanced or undercosted:

Lord Xavius - Love the concept of the card, but I would prefer if you could decrease his mana cost to 8-7 and his stats, so you can for 10-9 mana play him and use his inspire in one turn, kinda like Confessor Paletress.

Corrupted  Ancient - If you choose Card draw, it's way to strong, if you choose damage, way to weak. Make his stats higher (maybe 6/10) and change the card draw to 1 and  the damage to 4-5.

Druid of the Nightmare - Just weak, I mean compare to Boulderfist Ogre, the versatility is not worth it.

Druid of the Wild - Just love it.

Savage Moonkin - I like it, but it should only give 1-2 Moonfires, 3 Moonfires just makes it OP.

Darkspear Hunter - Compare it to Iron Sensei, it's not very good, make it a 2/3, maybe even 2/4.

Kael'thas Sunstrider - It's good, only I would wish you would make it a 6/10 or 4/12, because BGH and you don't want this card being removed easily, but I can understand if you want to keep it like that.

Enchanter's Staff - I think it's ok, but I also think you could make it a little bit more different and interesting.

Draeneni Cryomancer - Unless you don't have a very cheap card that freezes everybody, this minion is really weak, make it a minion with a very high health, a low attack and Battlecry: Gain +1 Attack for each frozen minion or the other way around.

Vindicator Maraad - Really like it.

Silver Hand Cleric Medic - As you wrote, should be a 3/5 mana minion with the same effect.

Silver Hand Protector - The Battlecry is weak, you can make his stats higher but I would prefer if you make him something else, like Inspire/Battlecry: give all minions Divine shield or Inspire: give random minion Divine shield, or something like that...

Tyrande Whisperwind - Weak and really just useless, especially in priest as a 6 drop. If you want to make her hero power related, then try something like "changing your hero power" concept (like Shadowform).

Corrupted Cleric - 3/5 for 3 is great, a 3/5 that casts a 3 mana spell for 3 is broken. Or change her stats or make her cost higher. Because I really like the concept.

Ner'zhul - I like it, but you need to think of more cheap/lategame totems that can be solely played (unlike Flametongue Totem), because this card is kinda like Inspire: Deal 3 damage to a random enemy.

Chain Heal - Overcosted, make it 4 mana no overload.

Dwarven Totemcarver - Really cool, maybe even "give a totem +3/+1"?

Totem of Wrath - Really good, maybe even too good, you could make it a 0/3.

Mannoroth - Mannoroth deserves much better, more "Destruction" theme, but your version is ok.

Risen Demonologist - I really like it.

Helboar - Should cost 2 mana, as you wrote.

Varian Wrynn - Make it 3/9, and I think you should make this card based of another character from WoW.

Darkspear Protector - 4 mana, gain 2-3 armor... not good, you should rethink the whole card.

Shattered Hand Orc - there is no point to his enrage effect, he has way low health, especially for his mana cost, make it maybe 2/5 atleast, even 2/6.

Flag Bearer - Or give it taunt, or make the attack stack, because now he is an Argent Watchman.

Cho'gall - He is just kinda boring, to much resemble Mogor.

Gurtogg Bloodboil - He is ok, could change his stats a little bit maybe.

Prince Malchezzar - Make him a 6/6, because now he is just a much better Boulderfist.

Auchenai Necromancer - Just make him 4/4 or 3/5.

Worgen Battlemaster - he is ok, but I don't see him used anywhere.

This is what I think of all the cards now, I am not a pro player at all, so don't take my opinions seriously, but I hope you will take some of my advice and can't wait to see all the cards you will come up with next.

Flash Heal + Card Draw.

Next: Hungry Dragon

So it's hard to make a card like Blessed Champion good, because the original card is just badly designed, especially compared to other cards like the new Seal of Champions. So I have decided to make it like that card.  You gain Divine shield. One of biggest problem of the original card, that if you wanted to remove an enemy minion, and used Blessed Champion, your minion would die, and you basically paid 5 mana and killed your own minion to get rid of something, the Divine Shield solves that. Also it costs less, so that's something, right? I know this card is still bad and situational, but it is much better than the original.

Next: Hogger

If they're nerfing Warsong Commander, then they should buff Grim Patron to a 3/5 at the very least.

The 5 health guarantees that it won't die to most 4 drops (Cough Piloted Shredder Cough).

Edit: I only changed the health, and kept the no less than (1) effect. I forgot about the exploit with Knife Juggler + Youthful Brewmaster, thanks SaltyDeagle81 for reminding me that.

Next: Light's Champion (if you can, just change this card based on the art, it doesn't make sense that a dude holding Sulfuras, simply silences a demon, so please be creative and change the whole concept of this card if you can)

Destroyer of Worlds

There are no 4 mana pirates in the game (I mean who plays Dread Corsair for 4 mana?) so it's nice to have one. Stealth and 2 health are ok, it guarantees that he wont die, even to stuff like Flame Juggler, unlike the original card, still pretty vulnerable but not that bad.

Next Card: The Mistcaller

Edit: Changed the card to be more like Holy Wrath.

It's a 2/1 beast for 1 mana which is already ok, and kinda going with the Dragonhawk theme, like Dragonhawk Rider, he has the ability to gain Windfury.

Next: Convert (if it was done already, then choose whatever you want)

For example: If your opponent hits you with a Salty Dog, you will summon a random 7-cost minion like Baron Geddon, War Golem or Dr. Boom. The secret doesn't trigger if you took damage from a spell, futigue, hero power, weapon or minion's ability (like Ragnaros the Firelord or Goblin Blastmage). Also, because there are no minions with those mana costs, I decided that if you take 11, 13-19, 21+ damage, this minion will be summoned (kinda like Shadow of Nothing or Worthless Imp):

If you don't have any cards left in your hands, his ability still works.