Hearthpwn

So the theme is unspent mana because, you know, it's pretty 'zen'. Here's the Disciple token:

Monks have two simple gimmicks:
1) Giving your hero Attack bonuses in ways that have no been done in the past, specifically in ways where they last during your opponent's turn, meaning that anything that attacks your hero takes damage (I put these in parentheses on the card just to make sure that was clear). To my knowledge, this has not yet before been explored in Hearthstone, but I think it's simple and straightforward enough to be believable, and I also think it's a cool reflection of Monks' martial arts.
2) "Battlecry and Inspire". There are a few cards with "Battlecry and Deathrattle", but "Battlecry and Inspire" has yet to be done and could potentially redeem some Inspire mechanics by introducing more Inspire minions that do also have an immediate effect even if you can't use your Hero Power in the same turn. Plus, I think it fits thematically as a reflection of monastic spirituality.

I think that this is particularly interesting for this assortment of classes (Druid, Priest, and Warrior), because they're all ones that are more well known for their later-game control-oriented decks (the current anomalous aggro Warrior meta aside), so giving them attack bonuses that apply during the opponent's turn could give them some interesting anti-aggro options. Druid may finally see some use out of Savagery or similar effects, Priest gets some exciting new aggressive potential, and as with Heroic Strike Warrior will get to stack the bonus on to its weapons for added power.

Ji Firepaw in particular might raise some eyebrows, but consider that, by the time in the game that you get to play him, most of the aggro decks that the effect hurts the most have either already won or weren't going to anyway. Further, it's important to keep in mind that if you really want to have that additional Inspire effect guaranteed, it's a turn 9 play, and a turn 9 play that has little immediate impact on the board and produces an (at that point) only moderately strong body is risky, especially since most of the decks that do well against Druid/Priest/Warrior's late game aren't going to be extremely bothered by their big minions taking only a point or two of damage for attacking face.

Well they all actually hunt a certain demon. And bring it with them, how handy. They are all able to kill that demon, but in that case they are not the best. All demons can be exploitet somehow... But im sure you find out yourself...

Mechanic: Swapping

Oppressive Death Knight - Paladin Class Representative

Kill copies of minions from your own deck. Great synergy with Deathrattle minions (Tirion Fordring, Anomalus, White Eyes, Aya Blackpaw, Deathwing, Dragonlord, Sylvanas Windrunner, Cairne Bloodhoof, Anubisath Sentinel, Twilight Summoner...).

There are 3 benefits:
(1) Kill a friendly minion and trigger its eventual Deathrattle for free;
(2) Keep the original copy in your deck;
(3) Have a dead copy ready to be Discovered by your Liches.

If your deck has no more minions when you play an Oppressive Death Knight, you summon a Forbidden Sepulture.

Even better than a Lich who discovers dead minions: an Oppressive Death Knight who summons them directly!

Lich - Mage Class Representative

Go fishing with your Lich to Discover some dead minions (yours and your opponent's ones, chosen randomly). You will probably find your previously played minions Oppressive Death Knights and Ner'zhul who can't wait to use their Battlecry again.

Summoned-dead minions are good not only for your Liches, but also for minions like Backroom Bouncer, Cult Master, Flesheating Ghoul, Knife Juggler...

If there are less than 3 dead minions when you play a Lich, the missing minions discovered are replaced by Lost Artifact cards.

If you succeed to play a Lich before 3 minions died, your hero can puts his/her hands on a free random weapon!

Ner'zhul - Shaman Class Representative

Unveil 3 minions from your opponent's deck to get a precious intel (opponent's strategy, key and tech minions...).

You also get the opportunity to add one of the discovered minions to the pool of dead minions. Your Liches will be glad to Discover it for you then.

When playing Ner'zhul, you might unveil Deathrattle minions from your opponent and trigger their effect for you (Savannah Highmane, Shifting Shade, Tomb Pillager, Darkshire Librarian...).

If your opponent has less than 3 minions in their deck when you play Ner'zhul, the missing minions discovered are replaced by Unguarded Secrets cards.

As long as Ner'zhul comes back from the dead thanks to your Liches, you can exploit your opponent's deck and get Secrets when it runs out of minions. Some Secrets have very interesting synergies with those 3 faction cards (Getaway Kodo), and Deathrattle minions (Redemption).

Warrior and Priest are two control classes that often reach fatigue. This is less frequent for Druid, but druid has resources to mill his opponent. Therefore, the general objective of my monk faction is to mill your opponent and put bad, Ambush!-like cards in their deck.

Hangover and Intoxication tokens:

Drunken Fighter, the standard tool for the general mill strategy of the class. The card is balanced around the Naturalize-Assassinate distinction which shows that drawing two cards for your opponent amounts to a 4-mana discount. They will likely have an answer to this in those two cards.

Alemaster is the standard "shuffle shit into your opponent's deck" card. It is a delayed 4 damage into face.

Chen Stormstout is the mill finisher. Its battlecry means that your opponent will take 15 damage upon reaching the end of his deck (which is accelerated by your cards) so they will likely die. Note that unlike "Hangover", "Intoxication" does not draw a card since that would necessarily be a fatigue one.

This faction is composed of Death Knights, undead, and other former Scourge agents and sympathizers that are... less than satisfied with the current management. Who put that orange guy in charge, anyway? So now they're unliving their undeath nowhere other than in the darkest corners of Gadgetzan. While not as numerous as the Grimy Goons, the Jade Lotus or the Kabal, their constant fighting keeps fueling the Scourgeous Beauties with new "recruits".

Needless to say, this faction's mechanics revolve around bringing people back from the dead. The below examples relate to minions only, but other cards could retrieve spells and weapons from beyond the grave.

Ebon Knight is not too good at raising the dead, but every bit of help counts. Both allied and enemy minions can be resurrected.

Keeper of Souls just follows on the tradition of other Gadgetzan tri-class Rares, providing a cross-class Discover option.

Gothik the Harvester can turn dead enemies against their former allies. Because that's how you take the streets.

(Frostmourne is a token only, not collectable, but marked legendary like the Ashbringer)

For this challenge, I wanted to make cards that would fit into existing deck archetypes, specifically Reno Mage, Freeze Mage, Mid-Range Shaman, Control Shaman, Dragon Paladin and N'zoth Paladin. Allowing these decks to get access to additional Freeze effects, they are able to excel at the control and attrition by slowing down your opponent or preventing trades and setting up lethal for your next turn.

Icecrown Juggernaut is my common card. It's a decently statted minion that might see play in any of these decks, assuming they have access to freeze effects. Nothing too fancy, it essentially casts the 0 mana spell Shatter when you play it.

Ancient Frostwyrm is my rare card. With only 12 Freeze cards in the current standard format, it's an extremely consistent Discover card. Interestingly, 10 of those Freeze cards come from mage, while there is a single shaman card and one neutral. You'll more often than not have a Frost Nova, Blizzard or Frostbolt to pick from, but will also likely see some underpowered cards like Ice Lance, Frost Shock, Freezing Potion orShatter. As a dragon it fits into Dragon Paladin, and as a 6 cost card it is purposefully difficult to combo with Reno Jackson.

Ner'zhul the Frozen King is obviously modeled on Tirion Fordring. A sticky Taunt minion that, even once removed, gives the player a powerful weapon. There are a lot of ways to play this card beyond using it as a big Taunt. Shaman's can hit it with an Earth Shock to remove it's Always Frozen condition, letting you attack with it. Any  of the 3 classes could destroy it with the Icecrown Juggernaut to unexpectedly gain access to the Frostmourne during your turn. And if that N'Zoth, the Corruptor comes down, imagine reviving both Tirion and Ner'zhul.