Learn English – A word for ‘make fun of’ but less intense than ‘ridicule’

He is dressed/behaving/acting unobtrusively because he doesn't want to [upstage] the main singer.

The synonym inconspicuously fits nicely too.

There are a number of words following that approach, each carrying different nuance, that may also work.

• humbly
• modestly
• circumspectly
• simply

There are also words that better capture the relative aspect of the behavior but are less descriptive, such as deferentially.

The words suggested so far for the second missing word work, although if you are still dissatisfied with what you have I can think of a few more.

There's always demonize

1. (American) To turn into a demon.
2. (American) To describe or represent as evil or diabolic.

Another good choice might be vilify. While it doesn't exactly mention it in the definition, I commonly hear it used to describe exactly what you're looking for.

1. to lower in estimation or importance
2. to utter slanderous and abusive statements against : defame

Edit:

I thought a little more about what you said about vilify, and how it doesn't really fit. It seems that the definition of villainize is closer to what you want.

1. To represent as a villain.