We don't talk enough about the Sauna Test.
Mike literally grabbed a pipe and tried to bash Billy's brain in to protect El, and then it backfired and Billy almost killed Mike, and all Will could do was... stand there.
We forget this because as soon as Mike grabbed the pipe, the camera prioritizes Mike, Billy and El. But Will was there. Lucas was there. Max was there. They watched helplessly as Mike nearly got himself killed trying to save El.
Will has his own memories of Mike being in danger and not being able to do anything about it. Watching Mike be a knight in shining armour and not being able to stop him from putting himself in more danger than he needs to be in.
Dustin has the cliff scene from season 1 but it's Will, Lucas, and Max that saw the sauna test.