Both El and Will are shown to be trapped in The Upside Down in season 2. El escapes the place by herself with her powers and manages to flee. Will tries to do the same thing and hides, but he doesn't get himself out. Mike finds Will and breaks him out of the trance. I think this really shows the difference of Mike between El and Will and who needs him more.

Compared to Will, Mike is much more relaxed about El's disappearance. Now, I'm not saying he doesn't care for her (he literally tried to contact her for 353 days), but he doesn't physically go after her or make an actual effort. He waits, and contrastingly, he did NOT wait for Will. He literally sees El through the window but STILL doesn't go after her. She tells Max that El is dead, when really, like Will, disappeared into The Upside Down. He insisted Will was alive, and that El was dead. 

In this, Mike is Venkman and Will is Dana. In the movie, Venkman is in love with Dana who who gets possessed by Zuul and controls the demon dogs. Mike is dressed as Venkman and him and Lucas fight about how he said he was Venkman first and when Will asks if there can be two, he says no. This whole scene is basically just a metaphor to show since Lucas isn't in love with Will, he can't be Venkman, but Mike can. (Duffers have also said they take inspiration from this movie).

Will is off and his friends don't seem to notice. All his friends except Mike. This shows that he can pick up on little details others can't because he pays more attention. Because he is in love with Will, and wants/needs to know he is okay. Mike says; "He's quiet today." to which Lucas responds with; "He's always quiet." Mike doesn't respond, because he and Will have a special bond unlike the others.

When Mike notices Will isn't at school, a shot is emphasised where he immediately rings the Byers on the school phone to which they don't pick up, which Dustin and Lucas don't do. This increases his anxiety, so he takes matters into his own hands and decides to show up at Will's house WITHOUT Lucas and Dustin. He gets let in by Joyce and stays with Will for nearly the entire season.

Jonathan and Joyce, the closest people to Will, share memories to try and get him back. Mike is also part of this group as he shares the memory of him and Will meeting for the first time. He says that asking Will to be his friend was the BEST thing he has ever done with a tear falling down his cheek. This is one of the only moments we see Mike actually cry in the show, which is very significant.

We figure out during the possession that Will's first word to Mike was YES after he had asked if he wanted to be friends; "You said yes! You said yes." This is a big contrast to El's first word to Mike which is NO.  This may symbolise that Will and Mike will end up together, and El and Mike will not.

This iconic scene is all about how Mike and Will understand each other so easily compared to the others. Will says; "Please don't tell the others, they wouldn't understand." which could potentially refer to his sexuality and that Mike just gets it. He understands, and so does Will when Mike says the line "If we’re both going crazy, we’ll go crazy together, right?" Will responds with no hesitance; "Yeah. Crazy together." This scene is also paralleled with a mileven scene in season 3 which we will get to later.

A zoom in in film is one of the most commonly used cinematographic techniques in history. They are used to draw the audience's attention to a specific subject, in this case, being Mike and Will's hands. This shows their intimacy, connection and most importantly, Mike's protection over his best friend. This can be seen in a romantic and platonic way, however there have been many zoom ins of romantic couples holding hands in this show. For example, Lucas and Max in the bus during season 2.

For the entire time Will is at the lab because of his seizure, Mike was with him, not his other friends. He stayed by his bed, even though it was probably uncomfortable sleeping in a chair. When Will starts to lose his memories, he still remembers Mike, which causes a proud smile to spread across his face. Additionally, Mike covers his ears when Will is screaming because he hates seeing his best friend in pain.

Mike says to El; "I never gave up on you. I called you every night for--" El interrupts and says; "--353 days. I heard." The thing is, he lied to her, because he DID give up on her. He told Max that she died like Bob. El returns after 353 days, which means that Mike missed a few days. Why? Because he was with WILL. He didn't try and contact her for that long because he is hopelessly in love with her, but because he feels like he is at fault and is worried about her. The writers WANT you to think he's in love.

Mike blames Hopper for hiding El all this time but most of us know Mike tends to project his own feelings onto others as seen in other seasons. He punches Hopper while saying "I don't understand! You stupid, disgusting, lying, you piece of shit! “You’re a liar, you’re a liar!" This could potentially allude to how he's confused about what he is feeling and feels like he is lying to El about their romantic relationship as it is not romantic on his part. However, this is just a speculation.

Will gets asked to dance, Mike encourages him. The look on his face tells that he immediately regrets it. @lesbianmindflayer on TikTok calculated how many seconds he was watching Will and the girl dance. It proved to be around 30 seconds long. There is also a parallel where Dustin is doing the same with Lucas and Max (he liked Max). This could show that Mike likes Will, although he doesn't realise it.