A lifetime ago, I made a custom Hearthstone expansion concept called The Trials Within Us, which was about overcoming personal adversity to achieve greatness. Each class would embody a flaw of some kind - Doubt, Arrogance, Fear, etc. - and that in turn would be related to a story from Warcraft lore. In The Burdens of Shaohao animated video series, Emperor Shaohao gained enlightenment and saved Pandaria from The Great Sundering by overcoming the Sha - manifestations of negative emotions - that burdened his soul and held him back.
The main selling point in terms of gameplay were the Trials, which function like reverse-Quests: the spell would provide you a Start of Game benefit, in exchange for an ongoing and permanent Burden you must deal with for the rest of the game.
If the title didn't give it away, I am brainstorming the notion of rebooting and overhauling the set for the modern age, and have put together some pieces to share with you. It's not much currently, because I'm throwing out most of it for being too old/weak, but feedback is welcome: turns out, I still enjoy the process of card-creation, and just might keep this up for a bit...in-between work, depression, and other obligations, of course.
For those who don't remember, Trial cards are Legendary spells with no Mana cost, as they are cast immediately when the game begins. They do not appear in your mulligan, are removed from your deck afterward, and cannot be generated in any capacity. The Burdens take the form of a black gem, like the orange gem for Quests: you don't hold them in your hand or interact with them directly.
I'll put what I have in class order, which now includes Death Knight and Demon Hunter!
The Death Knight
The Death Knight's Sha is Sorrow: Enslaved by the Arch-Lich, some Death Knights held onto their morals even as their bodies betrayed them. There would be no release from this cursed existence: they could never make up for their sins.
Story Legendary: Sir Zeliek. So strong was his faith that he could use the Light even after being turned into a Death Knight. Forced to become one of the Four Horsemen, elite guard of Kel'Thuzad. He would suffer relentlessly, unwittingly putting former friends and family to the sword and seeing them rise again as members of the Scourge.
Deck Archetype: Exploiting the Start of Game payout via "Summon a copy of this" effects like Shambling Zombietank, to quickly hit the 4-minion requirement. Reborn allows for you to trade whilst keeping the correct total.
The Demon Hunter
The Demon Hunter's Sha is Anger: Hardened by pain, novice Demon Hunters use their anger to steel their will and hone their body. Only a select few can survive the initial training intact.
Story Legendary: Leotheras, Blind Rage. Kael'Thas sent Illidan five blood elves to become potential Demon Hunters. Only one succeeded: three died, while Leotheras was driven mad by the horrible visions he saw. He fled the compound before being captured by the naga of Lady Vashj. Some say he was possessed by a literal demon.
Deck archetype: Big Spells, that summon high-Health Taunts or inflict damage without relying on a board of wee minions (that would otherwise be killed by the debuff).
The Druid
The Druid's Sha is Fear: A dark force seeks to consume the Emerald Dream from within. When a mortal has become corrupted by the Nightmare, there is no return; only death will set them free.
Story Legendary: Xavius, Nightmare Lord. The first of the satyrs, Xavius was transformed by Sargeras, the Destroyer when Queen Azshara sided with the Burning Legion. Despite this, Xavius remained a servant of the Old Gods, who eventually pushed him to corrupt Ysera and the Emerald Dream from within.
Deck Archetype: "Feral" Druid, attacking with your hero. Minions clearing the way so your attacks can go Face. Lashing out with Windfury, while recovering with Lifesteal.
The Hunter
The Hunter's Sha is Hatred: Her desire for vengeance pushes Alleria beyond the Dark Portal. She will come to know a thousand years of war, in the Twisting Nether.
Story Legendary: Alleria of the Void. Older sister of Sylvanas and Vereesa, she led an expedition into the Twisting Nether, only for a thousand years to pass from their perspective. She returned to Azeroth with her Army of the Light, to take on the Burning Legion as the first of the void elves.
Deck Archetype: A Hero Power-focused "sniper" fantasy, spreading shots to multiple enemies at once. Eat your heart out, Legolas.
The Mage
The Mage's Sha is Gluttony: Reliant upon the power of the Sunwell for centuries, the "Blood Elves" are addicted to magic. What lengths will they go to sate their appetite?
Story Legendary: Kael'Thas the Fel. So desperate to free the blood elves from magic addiction, Kael'thas Sunstrider sided first with the naga and their master Illidan for aid; later, he turned on them to join the Burning Legion, with promises of the power necessary to save his people.
Deck Archetype: Deathrattle Big Spell Mage. Purposefully allow your weak minions to die to leech their magical energy, thereby fueling your spells.
The Paladin
The Paladin's Sha is Doubt: Enslaved by the Iron Horde, their leader lost, her people betrayed; Yrel will take it upon herself to lead the draenei into the Light. But is she truly worthy of such a task?
Story Legendary: Yrel, Light of Hope. High Exarch Yrel hails from an alternate world dominated by the Iron Horde, seemingly doomed to suffer a horrible fate. Instead, she rose to prominence after the Alliance came to help defeat Garrosh's rebellion, leading her people against their tormentors.
Deck Archetype: 1-Versus-Many control, expressing the fantasy of being an unstoppable badass against the forces of evil.
The Priest
The Priest's Sha is Arrogance: "I consume the essence of the weak and foolish," the blade whispers in your mind. "You're not weak...are you?" Only the mad would dare wield such an artifact.
Story Legendary: Black Blade Xal'atath. Xal'atath is a sentient weapon said to be a claw of Y'Shaarj itself. Known to speak lies and drive people to madness. Eventually freed from the dagger by possessing a dead elf, she made a pact with N'Zoth. The primary antagonist of the latest World of Warcraft expansion, more details are unknown.
Deck Archetype: Shadow Face Priest, using your Hero Power in a race to win before you kill yourself.
The Rogue
The Rogue's Sha is Zeal: The Defias Brotherhood want what they're owed...but ambition will be their undoing. Revolutions demand attention, and that's exactly what they'll get.
Story Legendary: Vanessa VanCleef. Daughter of the former Defias Brotherhood leader, she eventually lead the organization in its efforts against the nobles of Westfall. Much later, she would put down her swords and poisons, helping to form the Breadbasket Guild to aid in the revitalization of the common people.
Deck Archetype: Coin Control Rogue, using Coins to trigger interesting effects beyond simple Mana-cheating.
The Shaman
The Shaman's Sha is Despair: Broken and lost, nightmares of his failure haunt the fallen Paladin Nobundo. The Light would not hear his cries; who would come to the aid of the former draenei and his people?
Story Legendary: Farseer Nobundo. A member of the "Broken", having become deformed and losing his connection to the Light, Nobundo prayed for guidance. He was eventually heard, but not by the Light: the Wind came to him, offering a connection to the elements and a way out of his despair.
Deck Archetype: Frost and Nature spells to stall/remove threats before the Frozen copies become a problem. Minions that don't benefit from being copied.
The Warlock
The Warlock's Sha is Violence: Binding his soul to the Burning Legion, Gul'dan will know power and blood as Darkness Incarnate. The Legion is infinite; their tolerance for failure is not.
Story Legendary: Kil'jaeden, Lord of Flame. Second in command of the Burning Legion under the Dark Titan Sargeras, the Destroyer, and creator of the undead Scourge. He was purposed with recruiting new allies to the Legion, and has held sway over several prominent characters over the years.
Deck Archetype: Self-Destruction, not of Health like normal but of one's other resources. Blowing up your Mana Crystals, burning your hand, destroying your board; etc. Turn-and-burn until you win, or the Burning Legion runs out of patience.
The Warrior
The Warrior's Sha is Madness: Voices haunt one's mind from all sides, yearning to break free from the shackles of sanity. Giving in could put this world in great peril; the level of destruction would be...cataclysmic.
Story Legendary: Deathwing, Worldbreaker. Neltharion fought alongside his dragon siblings to keep Galakrond, the Unbreakable from consuming the world. Becoming the Aspect of the Earth, he would grow to resent the task placed on him, giving the Old Gods a chance to corrupt the black dragon with promises of freedom.
Deck Archetype: Dragons and Fire, but also creeping insanity before surrendering to the madness and letting one's rage burst forth.
(Choose One option of Demeter's Sorrow)
(Choose One option of Maiden of Harvest)
(Choose One option of Persepholes)
(Choose One options of Life or Death?)
(choose one option for Underworld Courtship)
(created by Three Little Pigs)
(Created by Goldilock, Mama Bear)
(created by Cold Soup)
(created by Sinister Snowman)
(Created by Cursed Spindle and Poisoned Apple) 
(created by Pele)
(created by Go Slay the Orge)
(created by Disciple of Khaz'goroth
(Created by Deceived Siren)
(created by Damsel in Distress)
(created by Golden Straw Spinner)
(created by Ugly Duckling)
