Pool/Series 4 has some awesome cards, let's get into them! Realize that as of now, none of the decks below have been tested, but all have at least some reasonable theory behind them.
Please read this article to see some of the math on spending collector's tokens on pool-4 cards. I generally plan to spend all my tokens on pool-5 cards for collection reasons, with maybe 1 or 2 exceptions here.
Onto the cards!
She-Hulk
A card we were expecting long ago (Daredevil ended up being the season pass card instead of She-Hulk) to be the cornerstone of changing DeathWave into Surfer Girls.
In this deck, She-Hulk serves as a second card that could result in 2 large plays after turn-5 Wave. If Wave is the only play on turn-5, then on turn-6, She-Hulk gets a 2 mana discount from 4, resulting in a cost of 2 that can be paired with the other 4 mana card after Wave. Theoretically, there is a world (with 4 kills) that after Wave, we could play Death, She-Hulk, and another card.
That said, since then, Aero has been buffed and people have been running her and Magneto in the deck, so I am not sure what the best deck would be now. A quick example could be:
Aero is still a girl, so she fits nicely! We could also look to run Chavez for consistency pre-turn6 or Angel as well.
...some people really want this to work with the whole Sunspot/Infinaut thing...realize if you skip turn5, you cannot play both this and Infinaut, and Sunspot is generally not good.
Titania
I think this card is insane. I think this card is going to be nerfed. I do not know the best place to play this card, but please let me explain why she is insane.
First, let's talk about Green Goblin - when your opponent plays him, he's annoying, he takes up a slot on your board, and he's worth 3 power for your opponent. At least he costs 3 mana.
So what if, instead of doing that, I filled up your last slot with Titania (I play her + 1 other card on the same turn to send her over). You still lose that slot for the rest of the game, and on turn-6, I play anything there and get her back. She is now a swing of 5 power for me, for 1 mana, while still clogging that slot for you for the last few turns.
Or maybe I get stuck playing her into a full lane as a [1/5]...oh darn!
There's a lot of complexity past these 2 scenarios. What if she takes up your 3rd slot and I only have 1 taken up. You can play a card there and send her back to me, meaning you have 1 slot there. If I play there next turn, you end up in the same situation...so are you forced to play there 2 turns in a row? We get into some kinda crazy math situations based on what the power in the lane is also as we approach the last 2 turns.
She's perhaps not so great in a deck that wants to slam 5 and 6 drops on the last 2 turns? But in most other decks, she seems quite insane. Maybe I'm wrong, who knows.
Luke Cage
I think what Luke Cage does best is activate a 2nd On-Reveal for Wong in the ongoing deck - specifically Hazmat. The idea here is that we now have 2 parallel gameplans to make use of Wong for full board impact - not randomness and not into a single lane.
Here's an example deck that I like...and yea, I left 1 card out. Last card could be something like Armor, Mr. Fantastic, Rogue, Ironheart, Debrii, Cosmo or who knows what!
Absorbing Man
I'm 100% prepared to be wrong on this card. I know some players that I respect like this card, but I just don't see it. Let's start by comparing to Wong. 1 bonus power, and is played after rather than before the On-Reveal. He also gives you lane flexibility. The issue is, that as a 4 cost, you are either repeating an on-reveal from your turn-3, or you are playing him as one of your turn-5 or turn-6 plays. While I'm happy to play multiple low-drops on turn6, it's generally not because they have insane on-reveals. There are surely some cool, very niche, combos to be pulled off here, but I do not plan to spend collector's tokens on this.
Maria Hill
[2/3] is on rate for many 2-drops, which also means below-rate for "good" cards. Furthermore, would we ever want a random 1-drop over a Sentinel? I'm not convinced that we would....
Agent Coulson
This card looks like good generic value. A 3/4 is not great, but you know you will have 2 followup plays, if desired. The only specific deck that this fits into is a Collector/Devil Dinosaur one...but it may still fit into plenty of others as a flex slot. I would not personally spend collector's tokens on this.
Helicarrier
I don't play Hela/discard decks, so I'm not sure what to think of this. We don't want our blade to to discard some random junk this gives us, but it does just give us more plays...I'd say it's worth experimenting with in Hela, but I personally would never spend collectors tokens on this card.
M'Baku
This card seems super cool to me, but I don't think he's very good? 25% chance to not be a [1/2] that was drawn, not that a 1/2 is the end of the world. Best case is probably the final play into a Lockjaw lane on turn6, then comes back out for 2 power at end of game. That probably still doesn't make him good enough. I'm not going to put a list here, feel free to look up a Lockjaw deck! He's probably not worth your collectors tokens.
Attuma
Another card with not a lot to say. Clearly we need some synergy with him to play him - Armor, Professor-X, Venom, or Zero are the 3 that come to mind. the Attuma/Professor-X curve is probably the best. Also not going to make a deck for him, but those 4 synergies are cards to look out for. Steals Warpath's thunder in Destroyer decks (in an Armor lane).
Orka
Umm, not sure what to think about this. [6/14] is pretty good, honestly, but not sure how good it is. Not good for Jubilee decks for obvious reasons. I would not personally spend collector's tokens on this.
Anyway, that's all for pool-4 for now!