Villains monologue at us so much in videogames it's become passe. Oh, you're so evil you took over the radio station and replaced the friendly voice that's been guiding me since the tutorial just so you can tell me about your evil plan? Yawn. Use that radio to sing a song at me, maybe then I'll pay attention.
Sing during a boss fight and I'll pay even more attention. I'm not sure where this trend started, but the videogame boss who is so extra they can't help but perform an entire song-and-dance routine while kicking your ass has become a delightful trend—though not all the entries on this list are boss-fight songs. If it happened too often it would stop being surprising and lose all its power.
Which is also why games that are entirely musical don't count for the purpose of this list. You won't find Stray Gods, Billie Bust Up, Rhapsody: A Musical Adventure, No Straight Roads, People of Note, or Mortimer and the Riddles of the Medallion here. Only unexpected songs count, which is why you shouldn't read this list if you don't want their existence spoiled for you.
I've also left off...
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