Merry Buffmas indeed! (Argenport Gauntlet Grinder)

Helena, Skyguide has been restored to her former glory, and with that, we can build with Kira, the Prodigy again!

After theory crafting for a while, I determined for gauntlet there are probably just two sensible routes to go, either a mono Justice build or add Shadow cards and be in Argenport. Itstenz has a solid mono Justice deck on here, so I figured I'd work on an Argenport list...
First I'll discuss the core Justice cards of the deck:

We have a new addition, Mistral Messenger in the two slot. Wow, what an incredible card! a 2/2 flying and endurance on our turn means we can chip away for 2 (or 3 with Commando) every single turn and still have a blocker. On the AI's turn, we get a 3/3 that gums up the board against nearly every one drop and a lot of two drops as well. Of note, the AI prioritizes this card over Kira for torching, and that can play to our advantage.

Steyer's Eyes does a lot for a two drop. It can fix your power drops, ensuring you hit three, it can push for damage and lifegain, power up Kira permanently, and also occasionally shut down annoying void based decks. Unfortunately, you really have to get the campaign for this one, there is no alternative.

Kira, the Prodigy needs a bit of a build around, but a lot of the cards you need are ones you want to include in gauntlet anyway. We have 8 efficient one cost pump spells, and ways to recur Kira. Tricks are always great against the AI.

Rounding out the Justice units are some of the best three drops in the game (for gauntlet) and they need very little explanation.
Helena, Skyguide has a terrific statline, can buff Kira permanently and push damage. You only need to be careful when to take a turn off to pay that contract. Don't be afraid to just run her out when your hand and the board dictates it. When to use the contract can be somewhat skill-testing but you'll get the hang of it.

Unseen Commando can just win games on its own sometimes, particularly in multiples. It's devastating and a must answer unit! This deck can sometimes give it +1/+1 and regen, which makes it almost impossible for damage based removal decks to get it off the board. Sometimes it can be correct to play out another unit first instead to bait out that torch, so use your judgment.

Valkyrie Enforcer while occasionally cut-able, for a deck like this with fliers it is an essential include. Silence and a 3/3 flying body is never a bad thing.

Finest Hour is your standard include as the best one cost pump spell in the game.

Now onto the Shadow cards, which are really here to support the all-star Justice core...
For units and our market access, we run 2 Kerendon Merchant as I valued the deadly more than the flying as a ground blocker to stall, and I wanted a shadow market anyway because Vine Grafter needs it, and Grafter is the best of the two drop market cards. A 2/2 regen gums up the ground against aggressive decks, and whatever you choose from your hand to get that +1/+1 and regen will be a thorn in the AI's side. I would love to fit a 3rd Merchant but I can't find a cut. I think as it is, we have just enough market access. The only downside to Vine Grafter is it can be a little bit of a tempo hit to pay the ultimate.

Memory Dredger is an incredible value engine in this deck! It can recur any two drop, including ones that died in combat the same turn before we hit the enemy player. We have a lot of great two drops and this allows the deck to grind very well into the lategame as needed. Getting back Vine Grafter means another market pull as well!

For spells, we enhance Kira, the Prodigy with another one cost pump, Spiteful Strike also adding more lifegain to the deck. I made a judgment call that we have enough lifegain to run Dangerous Gambit as an unconditional two cost removal spell. I put a Slay in the market but I actually almost never need to pull it. I do not have unlimited testing time but that could be a candidate for a cut, I'd like to fit a relic weapon in there if I could.

The last maindeck spell to talk about does a ton of work here. It is a weakened combination of Dark Return and Suffocate but having that flexibility makes it invaluable. Opponent vanquished your 5/7 flying endurance Kira, well we get it back with Sinister Rumors. Need another market pull? Again, get it back. Need to kill a pesky two or maybe 3 drop that just attacked? Kill it. The last mode allows you to strip a spell from the AI deck. This is the least used mode but can be an option. I like to do it to the Harsh Rule decks, and occasional others as well when it looks like the first two modes are not needed. Great all-around card for a one cost spell!

For the market, I already talked about the possibility of cutting Slay for a relic weapon, maybe Hidden Garrote.

Furious Accusation is an interesting one. When I put it in, I thought maybe we could use some draw for the late game, but its main use has actually been a rare force the AI to draw and eat the 3 damage to finish it off! I have two 6 win runs with this deck, and one of them would have been a 7 if I had done the math. I pulled a unit instead, and died with the AI at 3. There may be another option for this slot as well though.

Vara, Vengeance-Seeker is a solid four drop that helps you race, and pops Aegis allowing you to better remove some pesky units.

Inquisitor Makto is just a solid 5 drop flier that you can bring in against the removal heavy decks if you really need to grind. It's not a common pull but great when you need it.

Makkar's Stranger can take over a game, especially when pulled with Vine Grafter and given regen. That ensures it will get two attacks, and kill their best two guys at a minimum. Usually by this point they are out of removal.

Overall, the market is the only place I would consider some alternatives.
I'm not going to go into much detail about the powerbase. The Marks offer undepleted power or fixing both for the cost of 1 power, which is great on turn 1. You need JJ first for turn 3, SS for turn 4 ideally and JJJSSS you will get fairly often to power up the Cylix and get an extra card.
Our powerbase is naturally slightly more depleted than mono faction decks would be, but it rarely is an issue and the shadow cards pull their weight for sure. I run 3 Justice sigils to make sure I can pull at least one with Steyer's Eyes.

Results, one loss due to pilot error as mentioned above to the Feln Ritualist boss (6 win run)
one loss to nakova & molot. No excuses here, I just got overpowered by a solid draw of cost decreased Dragons, and couldn't quite get there (6 win run) matchup felt 50/50.
one loss to Tavrod, Auric Broker. We flooded, they drew Units and weapons nonstop...

Every single other run has been seven wins:
Ancient Trinckets
Praxis Studies
A Shard Bargain
Spreading Venom
Nikki's Grab Bag
Feln Ritualist (redemption!)
Tavrod, Auric Broker
Highly Skilled (beat twice)
Power of Progress
Limitless Possibilities
Helpful Horns
Xenan Power
Labyrinth Treasury (VERY close game, stabilized after a nice removal top deck and got Makkar's Stranger down to clean up a few giant units! AI opened with Crownwatch Paladin then seized control of the air with 2x Valkyrie Enforcer and a Desert Marshal)

Important for a gauntlet grinder is speed of your wins, not just winrate. This deck has a great winrate, but the speed is also very high. It take approximately 7.7 turns on average to close out a game for me, the quickest was a turn 4 win against Price of Progress boss. People play at different real-life speeds so I feel this is the best metric to use. There were a few games where I was way ahead and not paying attention and missed pump spell/Helena lethal, so maybe you can get that win time down to 6.5-7 turns honestly haha.
I would suggest playing around with the market a bit, but I think the maindeck is probably set.

Enjoy and happy grinding!