Valkyrie - Asgardians, assemble

This one is very straightforward. Valkyries Weakness is her Ressource Package and Threat Mitigation, and to make a viable solo deck I wanted to mitigate those weaknesses. The way to mitigate her Ressource Package weakness is to just add one, using The Power in All of Us, Avengers Mansion, Quincarrier, Team-Building Exercise. It's nothing new, I only changed the usual Helicarrier for Team-Building Exercise, as she has enough Asgard-traited cards in this deck.

Asgardians, Assemble!

The nice thing about that Package is that Heimdall is much more affordable, so Valkyrie gets a solid Thwarting machine. He will usually not Chump Block but use his full 4 hp to thwart.

Nick Fury always goes into my deck if I use The Power in All of Us. A noteable exception is Ironheart. I usually always like to add her, but with Throg, Annabelle Riggs and Angela enough cheap allies are in the deck. Feel free to exchange her for another card.

Other than that, all available Aggression Asgardians (of course without Valkyrie) are in the deck:

Angela just synergizes with Valkyries Minion strategy, especially once Valhalla is in the game. Thor is an underrated card and one of the best allies, especially if Angela and/or Chooser of the Slain cater to his ability. Don't be afraid to sacrifice his tough for the attack if it means clearing the board. Jane Foster Thor honestly makes the cut so we have all the Asgardians. That being said, her ability is useful to remove tough from the villain, and with Boot Camp she can come in for 6 damage to the villain. Throg is a double chump blocker for 2, that's just very, very good. If you get Annabelle Riggs in your opening hand, I would not mulligan her away. Dragonfang and Valhalla are vital to Valkyrie.

Boot Camp is often an endgame card. This deck has a lot of support and upgrades to play, but getting the reach to rush the villian down is worth including it in this deck. It also synergizes with Thors Ability.

I think The Bifrost is worse than expected, I often do not play it because this deck has enough allies overall so you usually have one in hand, or a full board. Removing it and adding Ironheart is probably a good choice, but I just like how thematic this card is, especially if used to bring Thor in, uses his lighning ability to clear the board, and shout "Taste the Rainbow".

Threat mitigation

Heimdall and Nick Fury already push you a bit, but Smash the Problem is such a good card. Once Combat Training, Brute Force and Dragonfang are in the game, you pay 1 and exhaust to thwart for 5, that easily rivals what Justice can do. With her own Flight of the Valkyrior, you are actually quite consistent in the thwart department. Flight of the Valkyrior is actually a really good card to prepare an Alter-Ego Healing turn.

Death-Glow

Some other cards in this deck make sure your Death-Glow gimmick actually works. Brute Force is a tech card against Though Minions. It's still worth it to bridge the time until you get #Dragonfang, and sometimes you need to tackle a 5-Health minion. Of course it also makes Smash the Problem even better. While on paper it doesn't look great, it so often fills the gap in different (and otherwise frustrating) situations that I think you shouldn't switch it out. Mean Swing helps against those really high hp minions. And sometimes, you end up with Valkyrie's Spear.

General playstyle

In general, you should try to control the game with allies and (quite good) thwarting while building your supports and upgrades.

Some extra words on villain choice

As a minion-defeating specialist, I think Valkyrie isn't the strongest solo hero. You sometimes need to fish for minions. She can hold her own with this deck against most expert villains. But all too often I see people playing a specialist hero like Valkyrie, Thor or Hulk against a Villain that will obviously not let them shine. Do yourself a favor and play villains that let your hero shine. That doesn't mean it has to be easy, but make it FUN! Why play Valkyrie, Thor or Rocket against a Villain with no Minions and then lament that they are unbalanced or underwhelming? There are plenty of (actually very hard) villains like Ultron, Green Goblin Mutagen Formula or Zola, and/or side schemes that add 5-6 Minions to the villain deck.They are not easy, especially if played on expert (the minion-heavy villains are actually among the hardest in the first place), but I am pretty sure you have more fun making them harder but still have those fantastic minion-smashing turns instead of winning a game against Heroic Rhino but feeling bad doing it.