Loki is the best villain in the Marvel Cinematic Universe to date. That isn’t my opinion, it’s an objective fact. He has done battle with Thor in both Thor films, getting the best of him at least once. He has faced down the Avengers before they even were the Avengers. When the next time the team assembled, it is understandable that audiences wanted Loki to make a return appearance. Well, it turns out that he did, sort of.
To sum up, Loki was originally part of Thor’s dream sequence, probably to lay down the groundwork for ‘Thor: Ragnarok‘ that Heimdall (Idris Elba) ended up covering in the theatrical version. When ‘Age of Ultron’ was screened for test audiences, the feedback on the Loki scene prompted the studio to pull it. Apparently, Loki’s presence made some think that the God of Mischief was behind the entire plot. I have to admit, it would have been ironic if someone was pulling Ultron’s strings after Ultron adopted Pinocchio’s “Ain’t No Strings On Me” song for himself. The test audiences surely caught on that Ultron was acting without Loki by the end credits, but by then they would probably have been let down. I have to admit that I would have hoped Loki had a bigger role to play if he was established earlier in the film as well.
We should realize at this point that Marvel has the power to enlist big actors from their roster to appear for bit parts. I was surprised to see Chris Evans appear for just a few lines in ‘Thor: The Dark World’ as an illusion of Loki, but I shouldn’t have been. Stars from related movies make up the best of Marvel’s after credit scenes. It’s what they do. In this case, I would guess that the test audiences were confused primarily by wishful thinking. It wasn’t so much that they had good reason to believe Loki had a bigger role, it was that they wanted Loki to have a bigger role. That, or it could just be that Tom Hiddleston is so good at that mischievous smirk that it looks like he’s up to something even when he isn’t. Maybe he just smirked himself onto the cutting room floor.