Pool 3 Replacements (from my longer deck guide, link here)
Magik: Don't even bother man. Due to the flexibility of the Magik Control Shell, I would say that this deck can honestly serve as a budget list with replacements for the other Pool 3 cards if you are looking for something to try after you have just pulled Magik from Pool 3, but this deck oftentimes just doesn't work without Magik's extra turn and draw.
The Hood and Mysterio: I'm pairing these cards together because they are low cost, efficient cards that play well with Carnage. Low cost cards that can do fine in these slots are Korg, Iceman, Deadpool, Black Widow, Goose, Okoye, Scorpion, Scarlet Witch, or Daredevil.
Rescue: The newly buffed Jessica Jones is the cleanest replacement for a strong proactive 4 drop. It also has the benefit of being a better card to place into a Flooding location, against the new Storm decks that are starting to pop up. Definitely the easiest Pool 3 card to replace.
Captain Marvel: No card can match what Captain Marvel provides to this deck in terms of utility, but her slot can basically be filled by any big wincon card. You have the option of going bigger with cards like Iron Man, Hobgoblin, Gamora, or Magneto. You could go wide instead with cards like Blue Marvel, or Doctor Doom. Or perhaps you can play a different utility card like Sera or Spider Woman. When playing deck doctor in a game like Marvel SNAP, you are basically limited only by your creativity when it comes to finding good replacements.
Shoutouts to TLSG for covering this deck in a video