I'm glad I instinctively read Toad's with his MK64 voice in mind. With Rosalina, I imagined her trying to improvise a lullaby for the Lumas and then realizing it's not very good.
I think I read pretty much all of them as characters doing really good impressions of Waluigi or Wario. Like Mario goes the actual mile to make the nasal noises of Waluigi.
The last one I thought Rosalina was singing in some nonchalant way and then apologized.
The idea came about because it would be fun to imagine characters uncharacteristically saying things that another would say, and to me, the fun part is imagining Mario saying everything that Wario said during the Wario Press Conference. It's also based on the trick on colour-words being of a different colour than they normally are, like this: Orange, Green
Bowser Jr.: It's graffiti time, kids! I'll plaster my name all over this island!
Luigi: If you win, I hate you!
Baby Luigi: It's an exploration of greed, stench, and stubby legs through interpretive dance.
Wario: Now, this is funny: why did Banano fall out of the tree?
Toad: I lost to a bunch of losers!
Baby Mario: Fine! Take it! Get lost. And potty in peace!
Daisy: Stop touching the top screen. IT WON'T WORK!
Mario: GRRRRRR! I hate you.
Toadsworth: I still listen to records, but maybe you kids don't know anything but CDs these days...
Toadette: I'll bet half those gamers gave up. What a bunch of chumps! Peach: Have a rotten day!
Waluigi: This isn't funny, you idiots!
Vocaroo | Voice message