Variations of this deck - going wide with cards like forge + sinister turn 4, then beefing them up turns 5 and 6, has, with the various rotations in and out of the suggested pool 3 cards, brought me to infinite.
What the deck do:
Almost every card here is geared towards powering up your cards. You're going wide, but also a bit tall, in this way. You can keep pressure on, usually, at least two lanes, if not three.
There's a couple of ways to win, because who knows if you'll draw the right cards at the right time. This deck's flexible win conditions are one of it's strengths.
Substitutions:
As with any scientific test, CHANGE ONLY ONE VARIABLE AT A TIME. That means change one card at a time, play 3 to 5 games, and see how the change is working out. Don't do what I did and change a bunch of cards all at once and start an epic downward spiral from rank 99 to 70. Twice.
Specific Notes For Specific Cards:
1 COST:
Uatu is underrated - you can almost always either outright win the Raft for a free 6 cost card if you know it's coming. If he's in there turn 1, congratulations, you have an incredible advantage in knowing what locations you will start with. If the Raft appears, look at your current hand and save or drop him as needed. Uatu is still in my deck post infinite and it is still huge value. Agent 13 can be of similar help, but I don't run this deck with Agent 13 anymore. Only Uatu. He sees all, and he sees wins.
2 COST:
Forge pumps up Ironheart, Sinister, or whatever else needs a bit of oomph. Remember we will be adding +1 with blue marvel, and then another +1 with onslaught on same location as marvel. So turn two forge to turn 3 ironheart gives you at the end of the game, a 3/4 ironheart.
Forge/Sinister work very well. I almost always try for TURN 4 forge then sinister. This Forge is a 2/1 but makes whoever is played next +2. Sinister a 2/4 that makes another 2/4 (and his double also gets bonuses from locations that pump up cards with no abilities). Congratulations, with a forge amped 2/4 Sinister, you have placed 8 power in a lane on turn 4 with no other consequences (like discarding, etc), and that can be increased without risking Shang Chi ruining your plans.
Okoye beefs up everything else STILL IN YOUR DECK when she is played. Nice, but not necessary, and it will depend on what's left in your deck to draw. If all your low power cards are in your hand, there's not a huge amount of value for this.
Angela is solid all around, but I still don't understand why so many people run her. Still she's a great pool 2 card, and she improves herself, so if you're doing the climb, she can be very useful. Downside is you need to get her out early to maximize value, and you are telegraphing where you will be playing cards to your opponent. This means it's easy for your opponent to counter with a cosmo or storm to ruin your plans.
You can use this to your advantage however, and plunk Angela down somewhere you know you're not necessarily going to be focusing. I often will pop her down if I have nothing better, and see if I can put my turn 5 and 6 drops there. It's not expected, often. Mind games. I do not run Angela in my deck anymore, there's better cards for what this deck does.
SUBSTITUTION 2 COSTS
Adam Warlock is possibly the most powerful, underrated card in the game. No other card allows you to draw cards FROM YOUR OWN DECK (pre thanos, and even then, I have tried Thanos Gem Draw in this deck and it does not work well). That's an insane advantage. I used him quite a bit between 30-70/80. Everyone says he is the worst. They are wrong. He is appropriately tethered by the condition that you must be winning to draw the card, but otherwise he would be 100% completely god-tier.
Psylocke is a mainstay in this deck post infinite, and I have not found Adam Warlock as necessary, so he has been removed. Psylocke is still in here. It lets you get your 4 drop plans out a turn earlier (ie two two drops, or a four drop, on turn three).
3 COST
Captain America beefs up whoever is there, and onslught pumps up his ability as weI. I don't think he's ever moved out of this deck.
Ironheart is great turn 3 or 4 (with forge turn 3 etc), especially if you have three other cards on the field for max value. She's also a valuable turn 6 drop, with other cards, usually cosmo right after her, and depending on turn priority, don't forget.
Cosmo is a good boy yes he is. Who? Who shuts down wong? Who shuts down Zola Panther Combo? He does! Yes he does!
SUBSTITUTIONS:
Morph is fun, mam. If you're getting frustrated with the game, Morph adds some variety that just makes it...interesting. I dunno. He's a fun card. Could go for you. Could go against you. Adds variety. Swap in or out as you feel.
Bishop had a place in this deck before I hit infinite. Now, it's a bit harder to get that extra oomph out of him. Locations can help a lot with this, depending on what's hot. Reminder that Sinister and Brood's extra copies do not trigger a +1 for bishop, hence why he has fallen off. But I will usually switch out brood for bishop, depending on hot location or the way the day is going. He can be surprisingly game changing.
4 Cost
Run two two cost cards, or ironheart.
SUBSTITUTIONS
She's not the White Queen for nothing, and she'll not only tell you what your opponent has planned, she'll give you the card they generally plan to do it with.
5 Cost
Blue Marvel +1 to all but himself. This is a valuable win condition.
Iron Man is pretty OP, in general. Valuable win condition.
6 Cost
Onslaught is the only 6 drop. He is a 6/7 before Blue Marvel, a 6/8 with Marvel in another lane, and a 6/9 in the same lane as marvel or Captain America. Adds another +1 to captain america.
Flexibility is the key. You can win without Blue Marvel. You can win without onsluaght. You can win with both, in different places. You can go wide, AND a bit tall.
I still play this deck at rank 110, and it is still consistent. It will take a bit to get used to the various ways to win, and when best to apply them, but once you have played a bunch of games with this deck you will have a feel for what it can and cannot do.
Also please note: I don't snap anymore. I let my opponents snap for me, and then swoop in a win. Remember +2 is better than -4, and -1 is better than -8.
Half the game at ranks 50+ is knowing when the best move is to retreat.
Happy snapping!