Spire Shadows infinite power and infinite damage, such nice

This is mostly based on this deck

I tweaked it to add a bit of survivability in the early turns and with the release of Unleashed, it has become absolutely stupidly broken.

The biggest offender is the Valley Whisperer, probably even more broken than Spire Shadows. Once you've swapped the costs and powers, everything of value in the deck becomes unleashed with a cost of 1 or 2. When Kairos, Grand Champion is there, Riva, Crimson Blur costs 2, deals 2 then 5 dmg and you gain 7 power. Then you create and draw a copy of it. Arcanum's True Heart is also a nice addition as the AI has no idea of how indestructible works. If you've attacked at least once with it, you can safely Saloon Massacre and keep it alive.

Play Style:
You should redraw every time you have either 2 power cards in your starting hand or no Blazing Salvo / Merchant. Casting Spire Shadows is the number 1 priority every game. Do not hesitate to market trade for anything still with an original cost of 4 or greater with the exception of the Huntmaster Vikrum or Azindel, the Wayfinder which are fairly good without the swap.
Do not hesitate to board wipe with Saloon Massacre as soon as the AI gets a unit with 4 health. If it plays a unit with more, attack with anything that would die anyway, the AI usually blocks with the largest unit it has. Later on, if you haven't drawn anything good, focus on getting the Fall to Ruin. At that point, the AI usually has nothing in hand and you have much better draw potential as well as your market.

Edit:

Reworked the deck a bit. The winrate is now much better. The main problems were early swarm defense and mid game large threats.

The Devotee of the Sands is fairly good early block while helping the overall ramp up. It's especially good against Oni Ronin that seems to be included in 50% of the AI decks. Huntmaster Vikrum is very nice too. It's a pseudo removal that is unreliable, but quite good at taking care of the very large enemy units, especially flyers that are hard to deal with otherwise. Growing Sludge is a so-so card, but when swapped, a 5/1 for 1 cost that will grow indefinitely is often a game winner. The AI will very often underestimate the threat of a 1 cost stealth unit and not block when you attack with other units.

Also reworked the power base a bit to have less power cards coming into play depleted.

Other cards considered:
Xenan Adept
Aika, Whirling Death
Statuary Maiden
Questioning Devotee
Twinned Spiteling

Cards included in the decks should cost 4 or 5 and be of grade "Not so good" or above by themselves while having between 0 and 2 attack power. If you can't play a card before the Spire Shadows then it's not worth including it as your starting hand will be full of them as well as the first few cards you draw. You also end up at a much higher risk of getting power screwed once in a while.

Edit 2:
Moved Saloon Massacre to main deck. Early board wipe is very important for survivability. Reworked the power base, it's now much more consistent. Not sure about Grodov's Burden. I use it mostly to draw when late in the game. It can also Bury the Past relics and units which is always fairly useful.