Summary
Zabu as currently datamined is REALLY good. 4 cost cards can be a little awkward in Snap. In most circumstances you can only ever play one per turn and if you play them after turn 4 they just don't compare to opposing 5 and 6 cost cards. Zabu is going to change all of that because of his powerful Ongoing effect. His cost reduction will allow you to play two 4 cost cards per turn starting from turn 4 and on turns 6 (and 7) you can play three of them! Previously only Sera allowed playing two 4 cost cards in a turn(and even then only on turns 6 or 7). Not only that but when Zabu is in play along with Sera, you'll be playing 4 cost cards for 1 energy! That's absolutely crazy value and this deck looks to take advantage of that by doing a bit of a 4 cost card miracle on turn 6.
Gameplay
You'll want to play Zabu as soon as possible. If you don't draw Zabu by turn 4 you're pretty much screwed so we run cards like Chavez and Jubilee to increase the odds that we get Zabu in play by turn 4. After that the plan is to dump as many 4 drops onto the board as you can. If it's not looking good for you (no Zabu in sight) just retreat and hope for a better draw next game.
Goose is present to protect Zabu from Enchantress. However you still get beat by Rogue. Cosmo stops both but means you can't be as greedy with playing discounted 4 drops. Sometimes you'll want to play Cosmo on 3 and Zabu on 4 to protect Zabu because if he gets Enchantressed it's all over.
Assuming you play Zabu on 3 then your turn 4 will depend on if you have Sera in hand or not. If you have Sera, then you just play Cosmo or Goose + Rescue/JJ (because they need to be played before turn 6). On turn 5 you play Sera then on turn 6 you can dump your entire hand because all your 4 drops will cost 1 energy. If you don't have Sera in hand on turn 4 then you need to play enough cards that Dracula will still be guaranteed to discard Chavez on 6.
The Cards
The only truly essential cards in my mind are Zabu, Goose/Cosmo and Sera. I think I've explained why pretty well so far so in this section I'll just talk about the other cards. The 4 drops are all pretty flexible but I think there are some standouts that most iterations of this deck will want to run.
Chavez is not essential but I can't think of a good reason not to run her. Its critical you draw Zabu as early as possible and she helps with that so she's an easy include. She also has good synergy with Dracula and Shuri.
Shuri looks like one of the best 4 drops in the game with her effect able to generate insane value. She makes playing Chavez on 6 a whopping 18 power and the best part is that you could have played another 4 drop alongside Shuri on 5 to avoid losing tempo. Interestingly enough, a lot of 4 drops don't have particularly high base stats (JJ and Rescue) so you might find yourself wanting to sub in a card like Drax or Crossbones to hit that 16 power benchmark. Even White Queen or Thing might offer an appealing alternative.
Rockslide + Darkhawk are a pretty potent package. Add in Korg which can easily fit as an early game play or on turn 5 and you've got a strong combination of disruption and pure power.
Absorbing Man is my most anticipated new card at the time of writing this. His ability to copy the On Reveal of the last card you played opens up tons of interesting play lines. With Zabu in play you could play him with Jubilee to put 4 cards into the board in one turn. You could play him with Rockslide to send 4 rocks into your opponents deck and almost guarantee they miss a draw. You can also copy an important tech effect like Enchantress if your opponent splits their key Ongoing cards between two lanes.
Rescue is a high value 4 drop that I think is interchangeable with Jessica Jones. It could be good to run both but it feels like that's a little bit too many cards that telegraph your next moves to the opponent. Theres also the downside that neither Rescue or Jessica Jones really work as turn 6 cards so we'd want to limit ourselves to just one of the two. With Absorbing Man we have the option of having a second Rescue anyway.
Crystal is normally a pretty terrible card but I think she actually has a pretty strong use case in this deck. She can help us pull Zabu by turn 5 to occasionally salvage a game and she can reduce our hand size to guarantee Dracula discards Chavez on turn 6. Crystal into Zabu on 5 means you're going into turn 6 with nothing but 6 power on the board (maybe 9 if you played Cosmo on 3) and three 4 drops in hand plus Chavez. It'll be tough but depending on the 4 drops you play, you might be able to steal a win.
Dracula plays well with Chavez and since this deck lets us dump our hand on 6 it should be guaranteed.
Enchantress is just the tech card slot. She could be replaced with Shang Chi or Super Skrull. It could be correct to run multiple tech cards so you'll want to feel it out based on what you're encountering on the ladder.
Final Thoughts
This forthcoming archetype is pretty exciting. 4 cost cards have been the neglected stepchild of Snap cards so it's nice to see them getting some support. The best thing about this new archetype is that I think there's potential for different "flavors". Considering there are 4 cost cards with most other major keywords (Ongoing, OnReveal, Discard etc.) we could see a Discard deck that runs Zabu and some of Dracula, Ghost Rider and Hell Cow. Anyway that's all I've got for now. Later!