Marvel Studios recently confirmed that Loki was mind controlled by The Mad Titan Thanos in The Avengers (2012). And if you’ve noticed Mind Stone was successful in dividing Avengers, the Laboratory scene from The Avengers (2012).
In this scene, Mind Stone influences everyone negatively and it’s the special power of this Stone. The stone was also able to bring out two new Superheroes, Wanda Maximoff AKA Scarlett Witch and Pietro Maximoff AKA QuickSilver.
A theory by a Reddit User tekashi-samhain6596 says that Thanos controlled Ultron. After he was defeated by the Avengers in his first attempt with Loki, he set everyone to create Two Superheroes and made Tony have a warning about him. Wanda does the work perfectly and he sees a bigger threat and build Ultron.
Thanos used some sort of computered program to then control Ultron. Amd he failed too so, Thanos said in the end, “Ok, I’ll do it Myself”. This is a comic accurate theory, where Tony builds Arsenal to defeat Thanos, and in MCU He rebuilds Ultron and a Ultron Army with Wakandian Vibranium.
And then with an Ultron army and remaining Avengers, they fight Thanos. And then anyone of the Avengers or possibly Ultron tries to reverse effect the mind stone’s effect and make Thanos believe that Reversing the Decimation will be a good idea. Thanos has been using Mind Stone right from the beginning and has been spying on Earth. And that’s why he knows Tony so well, because he stole his database. And when Ultron failed he waited for the perfect moment (Odin, Ego and Ancient One to die, and for Avengers to break up).
There are many different theories for Avengers EndGame more than any superhero movie. I’ve read more than 127 different theories. I think I’m looking forward to read 14Million theories. When Marvel releases Avengers EndGame trailer 2,fans are going to get crazy and get ready for More theories. But still you’ll have to wait till 26th of April to see what actually happens.