Essentially a version of ongoing Destroyer that replaces Spectrum with Valkyrie, and some tech choices to fit that swap.
All our ongoing effects that add power still work after Valkyrie's effect goes off, so if you play her into a full lane that has no ongoing effects on their side, you'll just win the lane outright thanks to the free ongoing power. To that end, this list keeps a lot of the ongoing cards from the meta Destroyer list that add power to their lane. Mr. Fantastic is there since we actually buff his power by 1 with Valkyrie's ability, and as our only lane reach effect. It also makes stealing side lanes with Professor X a bit easier.
Yellowjacket serves two purposes mainly: play him into an empty lane before Professor X if you are stealing a lane without Daredevil information to try and ensure you steal it, or into your turn 6 to ensure you get the secondary lane (play him before Valkyrie to make sure his debuff is removed by Valkyrie's effect). Wasp can be subbed in here, but she's slightly worse at helping Professor X steal a lane and doesn't really do anything better in Valkyrie lanes.
Titania is often kept in hand for turn 6 to be played with Valkyrie. Be extremely careful if you try to play this card out before turn 6 - it takes quite a bit of practice and reading your opponent's plays to not have Titania turned against you in open lanes. That said, it can be really fun outplaying someone by pushing a Titania to their side and filling up their lane, while you keep two open spots on your side to bring her back on turn 6 (definitely watch out for this opportunity on locations like Mojoworld). Just remember, it stings to lose to your own card. To play it safe, just keep her in hand and play her after Valkyrie on turn 6 as another means of going over the top.
Valkyrie is almost always played on turn 6 as an alternative to Destroyer. Usually you will want to Professor X on turn 5 to lock up a lane completely, but Valkyrie on 5 can be an option if your opponent over-commits and fills up a lane by then (though this is likely to force an early retreat). Typically anyone that is staying on turn 6 after Professor X thinks they can beat both Destroyer and Spectrum, so Valkyrie is your means of getting them to stick around and pay more cubes. If you have Yellowjacket and a one-drop in hand, you can play up to 3 cards into a lane on 6, which will steal a lot of cubes from folks playing for raw power.
Otherwise you play your turns 1-5 a lot like existing ongoing Destroyer. Try to let your opponent take priority going into turn 6 if you can, otherwise you may not be able to flip a lane with Valkyrie if they also play into it. If you have priority and a secured Professor X lane, you're looking to play into a lane the opponent would assume is fully locked up for them and you don't think they'll play into again, or check if you can just brute force them with Destroyer (though if they can't beat a Destroyer they'll often retreat on 6).
This deck can have issues dealing with Devil Dinosaur decks (or more niche ongoing lists like Ronan the Accuser) because their ongoing powers are not affected by Valkyrie's ability. I don't think it's worth teching to try and deal with that weakness in this list; you'll probably just have to dodge those lists unless you can push them off a really bad hand. Adding Shang-Chi in place of Cosmo doesn't work that well, because they'll often have 2 Devil Dinosaurs anyway, and they are hard to steal a lane from with Professor X on turn 5. Similarly, be wary of ongoing buff decks like Patriot or Cerebro; Patriot's buffs still apply after Valkyrie, and Cerebro 3 doesn't mind at all if you set all their cards to 3 power. You also have to be careful of Wave on 5 decks, as a lot of them will drop at least 2 cards (if not 3 now with She-Hulk) on 6 while you can only drop Valkyrie - retreat if the lane you would play her in doesn't have enough cards on your side, or check if playing out Destroyer is worth considering instead.
Outside of those, I feel like Valkyrie is often a more threatening card than Spectrum, since any amount of raw power in a lane can be cut down to size. You can even sometimes deal with Aero plays on 6 so long as you double check how many cards are going to move; so long as your Valkyrie isn't outnumbered card-wise and you have one card buffing via ongoing (or just played last after Valkyrie's effect like Titania) you'll squash whatever power stack they put in that lane. Often times you'll just want to play in the lane they thought dragging you to would have helped them anyway.
The other nice thing about this list currently is that you play pretty well into Galactus, even if you don't see it coming. Since you should be stacking one lane a bit heavily like a typical ongoing Destroyer list, when they ramp into Galactus on 4 or 5, they will often either have priority against a lone card like Daredevil, or have to coin flip for priority against Captain America. You can even pass on 5 here because you don't care if they add an extra goblin to your side; so long as you have one ongoing card like Captain America or Ant-Man and can fill the lane on 6 after their cards flip, Valkyrie will crush whatever Death + X combo they drop on 6.