Marvel's What If..? definitely raised the stakes on the storytelling of the MCU when it introduced alternate realities into the table. For the pilot episode of the canon show, its title is What If… Captain Carter Were the First Avenger?, and it circled around Peggy becoming the recipient of the super-soldier serum. Later in the show, a monster with tentacles appeared through a portal. What is that, anyway?
What is the Monster in Marvel's What If..? Episode 1?
In Marvel's What If..?, Episode 1, What If… Captain Carter Were The First Avenger?, we see how things did not go as planned for Steve and it was Peggy Carter who had to take the procedure and become the First Avenger. However, she belonged to a time when women were disregarded and treated less than men, our heroine proved them all wrong. She sacrificed herself to push off a monster with tentacles to the portal.
When Hydra got the tesseract back, the Red Skull thought it would be best to summon a monster from another dimension to bring the nefarious plans of their organization into life and help them become invincible. However, when it came out of the portal, it easily devoured the people of Hydra, and Peggy had to fight it off using a shield and a sword.
She was successful, though, with the help of Stark closing the portal so she could push it inside and stop it from bugging the people she cares about, but that didn't mean she made it through, at least not until after 70 years.
Red Skull calls it the "champion of HYDRA," a monster with tentacles that would devour anything on its way. In the comics, the monster has a resemblance to Shuma-Gorath, an interdimensional being that will not stop to get anything the comes across. It's like Alioth, but this one has tentacles. Shuma-Gorath has been rumored to be one of the villains in Doctor Strange in the Multiverse of Madness.
But the difference lies in the monster's sentient. In the comics, it is but in What If..?, it seems not. It is also possible that this monster is a real hydra, one wherein you cut one head, two will grow, but for this one, cut one tentacle and more will come.
With the success of Captain Carter in defeating the monster, would we see the monster again? Let's see in the succeeding episodes of Marvel's What If..? and maybe we'll see it once more and know what fate it really faced.
All episodes of Marvel's What If...? Season 1 are available to stream on Disney+.