Eternals: 24 WTF Moments

Because the Thanos reveal wasn't WTF enough, it's also revealed that the Eternals aren't so much an alien race as they are synthetic android-like entities - or as Kingo calls them, "fancy robots."

In another exposition dump, Arishem takes Sersi to the World Forge where he shows her a vision of various prototype Eternals, effectively incomplete versions of herself.

Here she also learns that the Eternals were created to bring about the Emergence on many planets, but they have no memory of this because their memories were wiped after each mission and stored at the World Forge.

It's an interesting idea and certainly one few fans saw coming, albeit one that also doesn't feel sufficiently fleshed out considering its gravity.