Mat is entertaining for sure and it was interesting I agree but I don't think it's right. XD And yes SMG was definitely a great game (I actually like SMG2 more though).
Some of it was interesting and funny imo. Now that I watch this, I wish I didn't sell my Mario Galaxy game...I finished it, but not 100%. This makes me wanna play it again.
Again...although I enjoy his vids you can't use science to explain how fictional characters are related. Even though the writer originally intended for Peach and Rosalina to be related, he ditched the idea so canonically speaking they're not. And I'm sorry but to try and use spinoffs and multiple lives in a run is pretty ridiculous. If anything, this video taught me that Rosalina may actually be Mario and Luigi's sister instead (the brother with the green cap). We have no idea at what point in development Nintendo moved away from the related princess idea so you can't say "They actually are related but Nintendo doesn't want us to know".
And that would explain the end where Luigi and Rosalina are standing next to one another (just like they were as brother and sister in the story).
So based on genetics and in-game lore, it seems like Rosalina's parents MAY be Peach and Mario. But Rosalina's mother is dead, and Peach doesn't seem to be. Not to mention Rosalina and Peach look to be the exact same age. So what's the deal? Are they actually related? The answer is YES. Super Mario Galaxy explains how...even if it is a little difficult to decipher.