WARNING: Spoilers ahead, Do not read on unless you have watched What If…? season finale
1. The episode opens with Peggy talking about the evil mercenary Batroc, who we first met in Captain America: The Winter Soldier.
2. We also meet Brock Rumlow who happens to be assisting Captain Carter and Natasha to take down Batroc.
3. Natasha asking Peggy about her plans for Saturday was a small nod to Peggy and Steve’s date from Captain America: The First Avengers.
4. Natasha even makes an attempt to set Peggy up with Bernard from accounting. In Captain America: The Winter Soldier, Natasha made an attempt to set Steve up with Lillian from the accounts department.
5. There are even possibilities that Bernard who Romanoff was talking about was Howard Stark’s flamingo from Agent Carter.
6. We get mirrored visuals of Steve’s fight with Batroc when Captain Carter puts down her shield to go hand-to-hand with Batroc.
8. When The Watcher goes to pick T’Challa, you can spot Ego’s blue cloud all around the Dairy Queen, which also happened in Guardians of the Galaxy Vol. 2.
9. When The Watcher goes to get Gamora, you can see Eitri with her who we first met in Avengers: Infinity War. Here, they appear to be destroying the Infinity Gauntlet mold.
10. Tony Stark is seen expressing his desire to put a “suit of armor” around the world which is something he also talked about in Avengers: Age of Ultron.
11. In What If…? season finale Gamora can be seen donning the same battle armor that Thanos wore in Avengers: Endgame.
12. The Watcher blazons the team with the title of “Guardians of the Multiverse,”. This title sounds similar to a Marvel comics group that was called “Council of the Guardians of all Galaxies.”
13. Doctor Strange presenting Thor a beer at the pub a callback to the time that he made a cameo and gave Thor the never-ending beer in Thor: Ragnarok.
14. In What If…? season finale, when Doctor Strange casts a protection spell on all the guardians, you can spot the outline of Asgardian armor on Thor.
15. In a blink it and you miss it moment, when Doctor Strange drops zombies on Ultron using a portal, you can spot Zombie Captain America, Zombie Falcon, and Zombie Hawkeye attacking Ultron first.
16. The very fact that Zombie Wanda wasn’t able to stop this version of Ultron was because she kept on getting distracted by his resemblance with Vision.
17. Peggy makes a mention that she is one of only “three people” Natasha puts forth all her trust in. She’s possibly talking about herself, Clint and Yelena.
18. When everyone begins fighting Ultron turn by turn, the visuals that we get were very similar to the Avengers fighting Ultron’s minions in Avengers: Age of Ultron.
19. When Ultron unleashes the power of all infinity stones, you can notice that Nat’s shield which is made up of only metal cracks up unlike Peggy’s.
20. When The Watcher puts Natasha in an alternate universe, you can only spot Captain America and Captain Marvel are the only two Avengers fighting in the front. This implies that it’s the same universe from Episode 3 where the rest of the Avengers died.