Hearthpwn

The deck revolves around Emperor Thaurissan, Mind Blast and Prophet Velen, the combination of which provides 20 damage to the opponent's face which ignores taunt. The rest of the deck was built to both draw as many cards as possible to obtain the combo, and to retain board control. To this end, dragons function surprisingly well, as the tribe can abuse powerful synergies if you have a dragon in hand (which is more realistic a goal with high amounts of card draw), and has a powerful stat/mana-cost ratio which allows for a strong board presence throughout the game.

The broad spectrum game plan is to do your best not to lose board control. The combo will come in time, but the  pitifully slight removal suite of the deck means that board control will not happen if you don't fight for it. This does not mean your goal is to flood the board. Your goal is to keep 2-3 minions on the board at all times. Your second priority is to draw as many cards as you can so as to assemble the combo.

Broad spectrum tips:

• Try not to use more than 1 Holy Smite on minions per game. More often than not the second one is more useful for obtaining lethal than board control. 
• Always keep 1 dragon in hand. The ONLY exception to this rule is if Alexstrasza is the last dragon in your hand and you are forced to use her to heal your face so you don't die.
• Do not play Bloodmage Thalnos for cycling. He can be used to buff a Holy Nova to help clear a board of 3+ *non-hero power* minions, or to boost your combo damage to obtain lethal. Don't even play him to buff a Holy Smite. It never ends up being worth it.
• Don't play Emperor Thaurissan unless he hits at least two of the following: Prophet Velen, Mind Blast #1, and Mind Blast #2. Holy Smite also works but only if you have one of the aforementioned cards in hand as well. You don't emperor two smites.
• If you have two minions of similar cost (i.e: Blackwing Technician and Acolyte of Pain) in hand, play the one which better develops the board first.
• If you run it, don't play Northshire Cleric unless you can heal one of your minions the turn you play it. Northshire Cleric is a source of card draw. Don't play it if it won't draw you cards. Exception: Turn one go first Northshire Cleric if playing an active Wyrmrest Agent on turn 2 is possible, and only vs shamans, hunters, paladins, and warlocks.
  
• Count to make sure you don't have lethal every turn. This deck's burst potential will often surprise the user just as much as the opponent.

At first this sounds silly, because the main combo of this deck is fairly straight-forward. Play Prophet Velen, 2xMind Blast, and maybe a Holy Smite, deal 24 damage to face, and win. The deck is far more intricate than that.

 

First and foremost: This deck has a magic number: 15

 This is not only the health your opponent is left with after being hit with Alexstrasza, but is also the amount of damage the deck is most capable of dealing to the opponent in a typical game via spells etc, given that we only have 10 mana. The following are the ways the deck manages that:

1. Bloodmage Thalnos + 2xMind Blast + Holy Smite
2. Azure Drake + 2xMind Blast + Holy Smite
3. Blackwing Corruptor + 2xMind Blast + Holy Smite

Note: All 15 damage combos require a Holy Smite. That's why the second copy is so valuable. Similarly, try to save at least one of the three aforementioned minions so that you have the ability to deal 15 damage. Bloodmage Thalnos is usually the most useless outside of combo, so he is the one you want to try to save the most.

 

Standard Lord Velen has a couple of other magic numbers, though none as commonly relevant as 15:

• 40: Prophet Velen + Bloodmage Thalnos + 2xMind Blast + 2xHoly Smite Assuming all of the aforementioned are hit at least once by Emperor Thaurissan. This is the deck's damage ceiling, and is only needed vs control warriors.
• 24: Prophet Velen + 2xMind Blast + 1xHoly Smite Assuming two of the aforementioned are hit once by Emperor Thaurissan
• 20: Prophet Velen + 2xMind Blast Assuming one of the aforementioned is hit by Emperor Thaurissan.
• 18: Prophet Velen + Mind Blast + 2xHoly Smite. Assuming one of the aforementioned is hit by Emperor Thaurissan

From here down no Emperor Thaurissan ticks are required.

• 18: Bloodmage Thalnos + 2xMind Blast + 2xHoly Smite
• 15: We went over this one in depth.
• 14: Holy Nova + 2xMind Blast + Holy Smite OR Prophet Velen + Mind Blast + Holy Smite

Anything dealing less damage than 14 should be easy to recognize after playing 5 or more games with the deck, and thus shouldn't need pointing out.

Lets get the easy 1/3 out of the way first: If your opening hand does not have any dragons in it, mulligan everything to get a dragon.

For the second 1/3: If your opening hand has one dragon, keep it and mulligan any cards that cost 4+ OR do not have dragon synergy.

Now for the hard 1/3: If your opening hand has more than one dragon, keep the lowest costed dragon UNLESS one of the dragons is Twilight Welp. In such a hand, keep the second lowest costed dragon as well. Then, proceed to mulligan any cards that cost 4+ OR do not have dragon synergy.

The following modifications are ways to alter the deck based on the meta:

 

• Twilight Guardian --> Elise Starseeker

This change is made when the meta is full of slower decks like Control/C'Thun Warrior, N'Zoth Paladin, Control Priest, Reno-Lock, and Grinder Mage. The goal is that if the opponent heals for so much that the combo is no longer realistic, you retain a game plan by turning all of your dead combo cards into legendaries.

 

• Twilight Guardian --> Defender of Argus

This change provides a boosted win-rate against highly aggressive decks (+5%) but creates consistency issues against control decks, as you have 1 fewer dragon in the list, and need to have an established board for argus to be good. Often, playing him against a control deck just gets your board wiped. All in all, this is a tech/budget decision, but not my personal preference.

 

• Northshire Cleric --> Netherspite Historian

This one needs some testing, but given that Northshire Cleric only tends to draw 1 card per game, it's possible that Netherspite Historian would be more useful, given that he draws a dragon, which can provide much needed late game. Still, this is a combo deck first and foremost, so drawing a card from the deck might be more powerful than a conditional dragon discovery. This change would also likely be made in control oriented metas

Preliminary testing makes me believe this to be a viable substitution, but a lot more of it will be required before I know which one seems to net a higher win-rate. Netherspite Historian provides better late game (as expected), but conversely, the late game dragons it provides often do not get played over the course of a normal length game. On the other hand, it seems it is easier to have a dragon in hand than a damaged minion on the board, which is a point in the historian's favor. These are just my observations so far. I am not sure which minion is better for the deck yet.

This change was made to the deck.

 

The following changes are for those who lack certain cards, and seek replacements:

Disclaimer: All of the following changes will have a net negative impact on the deck's win-rate. You have been warned.

 

• Bloodmage Thalnos --> Loot Hoarder/Netherspite Historian (if you have it)* Northshire Cleric

The immediate question I get is "Why not Kobold Geomancer? What happened to 15?" The answer: I've tested it.

In a combo deck like this the cycling is more important than the spell damage. You just use the Loot Hoarder as an early game minion much like Acolyte of Pain now.

*The Netherspite Historian also works in this slot, as it provides a form of "card draw" and allows the deck to play at a slightly higher tempo. The historian is slightly inferior to thalnos as he does not provide spell damage for Holy Novas (which is relevant far more often than you might think). The dragon you discover is likely to deal about as much damage over the course of a game as thalnos adds to your combo (4-8 dmg average), and the potential to get Chillmaw occasionally makes up for the lost AoE potential.

Northshire Cleric provides card draw, and in absence of thalnos, more cycling is the most important thing.

 

• Chillmaw --> Excavated Evil

You lose a dragon and a 6/6 taunt body, which hurts consistency (-5% winrate). Still, Chillmaw acts primarily as a board clear, so it's only logical that he gets replaced with one.

 

• Alexstrasza --> Malygos/Ysera/Netherspite Historian*

Malygos does increase your combo ceiling (if he survives a turn), but he often does not, which means that Alexstrasza's battlecry often does more, and Malygos cannot serve the dual purpose of healing you.

*Netherspite Historian has not been tested as a replacement, but the idea is that maybe he could discover Alexstrasza or Malygos while providing an early game bodyAlexstrasza's effect is not replaceable by another high end dragon (though Malygos tries). Ysera also sort of works in this slot, as Ysera can provide two different extremely cheap spells which essentially read "deal 5 damage," but that is an un-reliable multi-turn set-up. Either dragon is a workable change, but results in damage to the win-rate.

 

• Netherspite Historian --> Northshire Cleric

Netherspite Historian does something unique in providing this deck with a mix of early game pressure and late game stopping power by discovering dragons (an inherently powerful tribe). The closest we can come to replacing it is with a similarly costed minion which provides card draw, in hopes of substituting an increase in pressure via board presence with an increase in pressure via decreasing the amount of time it takes you to assemble your combo. This change in tactics still comes at a cost, as Northshire Cleric doesn't consistently draw enough cards to compare to the likes of Malygos/Ysera/Deathwing/Hungry Dragon (if you discovered him via a 1/3 historian, it means the 1/3 can usually deal with the 1 drop) vs control.

All in all, this change has a relatively minor impact on your winrate (negligible vs 8/9 classes), but against warrior it can drop your win-rate by as much as 10%. I have been extremely impressed with the historian's ability to put enough pressure on warriors (even c'thun warriors) as to keep them within lethal range of the combo.