What If…? Episode 4 featuring Doctor Strange, packs several Easter eggs and subtle hints at how time-travel and the alternate timelines of the multiverse work. The latest episode established concepts like "Absolute Point in Time," splitting the universe into two timelines.
The episode introduced Supreme Doctor Strange, who is confirmed to appear alongside Captain Carter and T'Challa (Star-Lord) in the What If…? season finale. Furthermore, Episode 4 marked the second appearance of Shuma-Gorath in What If…? Which hints at the character's appearance in the live-action.
The conclusion was also left at a cliffhanger with regards to Supreme Doctor Strange's fate after his universe collapsed when he brought Christine back to life. The episode also contained a surprising interaction between Sorcerer Supreme and The Watcher.
Here's a list of Easter eggs and theories from Episode 4 of Marvel's What If…?
Radical Hemispherectomy
In the episode, Christine Palmer states that Stephen Strange is recognized for a radical hemispherectomy surgery in an exposition dump. The procedure involves the separation of half of the cerebral hemisphere in neurosurgery.
This foreshadows when the Ancient One splits Doctor Strange into two versions in a different timeline but the same universe.
Cagliostro
In What If…? Episode 4, Supreme Doctor Strange meets a sorcerer named O'Bengh, who claims to be the librarian for the book of Cagliostro. In the comics, O'Bengh was also speculated to be Cagliostro, who uses the text of Darkhold to achieve immortality. In the MCU, Cagliostro has been mentioned before as the creator of the relic known as the Eye of Agamotto (which housed the time stone).
Although Cagliostro is primarily a villain in the comics, in the episode, he was a wise old sorcerer who tried to guide Strange into doing the right thing.
Characters Strange absorbs
All the characters Supreme Doctor Strange absorbs to get enough power to bring back Christine had references to comics and other sources.
Here are some characters that the author spotted:
Gnome
The very first creature that Strange absorbed was a living garden gnome. This could be a reference to Gnomes in the comics. They were an alien species from Asgard and Elseworld.
Batwing
A vampire bat-like humanoid creature was also absorbed by Supreme Strange, which could potentially be Jimmy Santini (Batwing) from the comics. Batwing first appeared in Untold Tales of Spider-Man #2.
However, the creature could also be a Charniputra, who are gargoyle-like vampire creatures from the comics.
Raven
Strange also absorbed a mystic bird-like creature. While some viewers thought it to be the famed Phoenix force from the X-Men comics. It is unlikely that Marvel would drop such a big X-Men easter-egg in What If..? However, it is plausible that the creature depicted Red Raven from the comics.
Thor: Ragnarok's dragon species
Dragons will be heavily featured in the upcoming MCU film Shang-Chi and the Legend of the Ten Rings. However, the dragon showcased in What If…? Episode 4 is similar to the Fire Dragon from Thor: Ragnarok.
Jormungand
Episode 4 also had a giant serpent-like monster who Strange absorbed for its powers. This creature is likely to be Jormungand (or the Midgard serpent) from the Nordic mythology and Thor Comics. In these sources, the snake is the offspring of Loki.
Vishanti Spell
While in the MCU, 2016's Doctor Strange established that the sorcerers draw their powers from other dimensions. In the comics, the trio of Vishanti acted as patrons to the sorcerer and sometimes even gave them powers.
The "good" version of Stephen Strange refers to these gods in his protection spell that he utilizes against Supreme Doctor Strange.
Shuma-Gorath
Strange also absorbs the powers of a variant of the tentacle-based monster shown in the first episode of What If...?
How does Doctor Strange have the Eye of Agamotto and presumably the time stone in Spider-Man: No Way Home?
Several viewers wondered why Doctor Strange had the Eye of Agamotto, which used to house the time stone, in the NWH trailer. Furthermore, Strange acted out of character when he nonchalantly helped Peter, which ultimately led to the convergence of some universe.
Episode 4 might have hinted at how Stephen seems strange (pun intended) in the NWH teaser trailer. It can be theorized that the Sorcerer Supreme viewers see in the footage is the Supreme Doctor Strange from the What If…? reality.
This might be plausible as it has already been established that the What If…? Doctor Strange can travel between universes.
How does Vision Return to the MCU in Doctor Strange: Multiverse of Madness?
As established in the latest episode, a Sorcerer Supreme requires much power to bring someone back to life. This could hint that MCU's Doctor Strange might absorb Scarlet Witch's power as Wanda is expected to be the initial antagonist of the movie.
It is plausible that Strange absorbs some of Wanda's powers to bring back Vision, Tommy, and Billy.
Supreme Doctor Strange is confirmed to be part of the upcoming What...If? Episodes (including the finale). Furthermore, Strange will appear in Spider-Man: No Way Home and Doctor Strange: Multiverse of Madness.