How do you make Boss remixes

[Ronald Poe]

I'm an Electronic musician and I'm at least decent at ambient music.  How would one go about taking an ambient theme (stage or character theme presumably) and remixing it into a boss theme? You know like Donkey Kong 64 did for its soundtrack. I've already searched the internet for tips but didn't find much at all. 

Here's where I got the idea from.
https://tvtropes.org/pmwiki/pmwiki.php/Main/BossRemix

Someone else's example.

 

[LemonheadVGM]

This might be late, but something I would do is add more energy to the song to convey the type of feeling the boss conveys. If you want a frantic theme or an energetic theme, increase the tempo/pulse and re-harmonize it accordingly. If you want a menacing or ominous theme, slowing the track down and adding a more spaced out pulse should do the trick. I hope this helps at least a little bit.