Warning: The following contains spoilers for Secret Invasion on Disney Plus.Though the Skrulls were introduced in Captain Marvel, they return to the Marvel Cinematic Universe in Secret Invasion, and with their return are also some MCU Easter eggs and callbacks to earlier movies. This is especially true in Secret Invasion episode 2, which sees a list of DNA specimens in a Skrull computer. Those DNA specimens include Frost Beasts from the Thor movies, Groot from the Guardians of the Galaxy, and Cull Obsidian from Thanos’ allies. The list also has Extremis on it, which isn’t a species, but instead, a serum developed in Iron Man 3.
Just what the Skrulls plan on doing with this Extremis sample might seem like a mystery, but the answer lies in Marvel Comics. In order to understand how the Skrulls might want to use Extremis, it’s important to understand exactly what Extremis does and how it can help the Skrulls. The presence of Extremis along with those three other samples offers up one huge clue for Secret Invasion viewers.
What Is Extremis?
Extremis is a serum initially developed by Aldrich Killian and Maya Hansen to help those with lost limbs. As Killian points out to Pepper Potts, “Extremis harnesses our bioelectric potential,” and that potential can be used to do many things. Those injected with Extremis are stronger, faster, can regenerate lost limbs, and even produce fire. The formula, however, is initially unstable. It sees those who have been injected with Extremis as part of the trials combust.
After Pepper Potts is injected with Extremis, Tony Stark finds a way to stabilize the formula, saving the love of his life. It’s created using nanotechnology, which also provides the basis for his later Iron Man suits, so it’s an area in which he has plenty of expertise. His stabilization of the formula in Pepper Potts, however, means that she’s never seen using the abilities from Extremis beyond the events of Iron Man 3.
Where Has Extremis Appeared In The MCU Since Iron Man 3?
Since first appearing in Iron Man 3, Extremis has only appeared in one canon Marvel Cinematic Universe project before Secret Invasion. Its last appearance in the MCU is in Shang Chi and the Legend of the Ten Rings as an Easter egg as well. There, it was being used by one of the fighters in the illegal super-powered cage matches. It has, however, also occurred in tie-in materials for the MCU.
Extremis also appeared in the book The Wakanda Files: A Technological Exploration of the Avengers and Beyond. The book is made to act as an in-universe document compiled for Shuri (Leticia Wright), who is interested in the technological advancements witnessed by Wakanda’s War Dogs (or spies) out in the real world. Extremis is one of the advancements listed in the book, and Shuri’s notes conclude that it should be studied further because, despite the dangers, Extremis still had potential.
Extremis has also appeared in one more place, the MCU canon-adjacent series Agents of SHIELD. Though the show originally spun out of the events of The Avengers, it eventually evolved to be in its own timeline thanks to time travel occurring in multiple seasons of the show. There, Extremis was used as part of a cocktail by one of the factions of Hydra still left in Project CENTIPEDE. Extremis, along with several other items, were injected into those experimented on by a device resembling a centipede on their arm. It was also experimented with and injected in Daisy Johnson (Chloe Bennet) to enhance her Inhuman abilities.
Extremis, as a result, has shown some exciting potential in the MCU before it was experimented with by the Skrulls in Secret Invasion, but those experiments could see it play a big role in the Disney Plus series moving forward.
What Role Does Extremis Play In The Skrull's Experiments?
The Skrulls are probably not interested in the Extremis enhancements for strength or speed because they’re already superior to human beings in that regard. Instead, they’re likely interested in how Extremis increases heat in the body, and more specifically, it allows the host to create fire. Aldrich Killian shows that he can breathe fire. Pepper Potts is able to walk through fire without harm. Both of those would interest the Skrulls who appear to be experimenting with the creation of Super Skrulls.
In the comics, a Super Skrull is initially created after they clash with the Fantastic Four. DNA samples from each member of the Fantastic Four allow the Skrulls to create synthetic versions of their powers for one Skrull, called a Super Skrull. This is a big deal for the Skrulls because they don’t evolve or mutate to have powers like humans do in the comics. That also appears to be the case in the MCU so far.
The DNA samples shown as an Easter egg in Secret Invasion episode 2 are analogous to those Fantastic Four abilities that are used for the Super Skrull. The Thing’s strength is analogous to Cull Obsidian’s, Mr. Fantastic’s ability to stretch is similar to Groot’s ability to grow his limbs, and the Frost Beast with its ability to be frozen for long periods of time is likely meant to be analogous to the Invisible Woman’s force fields. Extremis provides the same fire as the Human Torch. That means Extremis will play a role in creating the first Super Skrull in the MCU.
The collection of DNA samples means that the Skrulls have been experimenting for years. They’ve likely had numerous failed experiments in the past, but with Gravik’s determination to take over the planet, he could be the first successful Super Skrull with the abilities given to him by those different DNA samples.
New episodes of Secret Invasion are available Wednesdays on Disney Plus.