Why is Rosalina so old? Why do enemies spit out star bits when killed? Why do getting so many star bits give you an extra life? Simple. Star bits are made of life force. Rosalina's diet is star bits, you are physically knocking the life out of enemies, and collecting all of those bits gives you more life.
This makes further fridge brilliance when you remember Rosalina's storybook, when the comet was filled with star bits. Many scientists think essential building blocks of life came to Earth from comets.
To anyone who may question where the mansion in Ghostly Galaxy came from, the answer does come from thinking about it. The simplest answer is that the Boos found in the level made the mansion like they created Luigi's Mansion.
The levels are too small to be galaxies, or maybe you're simply visiting the part of the galaxy that has power stars.
This can especially be the case when you consider how many levels, most notably the Comet Observatory, are floating over a gigantic celestial body.
Plus there are largely inaccessible planets shown throughout some of the levels. There's also a good chance that some of the other planets in the galaxies are just out of view.
If you do two games, one with Mario and one with Luigi, Luigi actually gets more stars than Mario. In the main quest, Luigi finds 3 stars to help Mario, bringing the total stars Mario finds down to 118, not counting all the stars the Toad Brigade found. In Luigi's quest, you play as Luigi and have another Luigi show up, thus bringing the total stars Luigi finds in that game to 121; add that with the total from the last quest, and Luigi's grand star total is 124 to Mario's 118.
Ever wonder why the first characters you see in space are rabbits? A common Japanese belief is that if you stare at the moon, you will see the shape of a bunny, hence why space bunnies are in this game.
And then there's the Chinese legend of bunnies on the moon, as well as the image of a bunny on the moon's visible surface.
Cosmic Luigi has the same voice clips as Cosmic Mario. One wonders why......until one realizes that they are controlled by the same Cosmic Comet......
While playing as Luigi, if you grab the Boo mushroom, you'd see that in his Boo form, Luigi looks quite uncomfortable. Luigi's afraid of ghosts. Therefore, he's actually scaring himself while in that form.
The repeated sequence of notes in the Ghostly Galaxy theme (the one that starts the song and continues to play throughout it) is a D-E-A note sequence. Put the first note of the next sequence on it and it spells D-E-A-D. Seems all the more fitting that it plays in a haunted house level.
The Garden is easily the most mysterious location in the Comet Observatory and it's not exactly made clear why it exists as the highest dome in the observatory. Young Rosalina expressed how she wanted to return to "the house by the hill", and often refers to said hill. The Garden could potentially be Rosalina's attempt at recreating the place on her planet that means the most to her; the hill.
Possibly unintentional, but the colors of the baby Luma and Rosalina's hair resemble cosmic latte, the scientifically-determined average color of the universe.
There's a saying that rabbits can die from loneliness. Now, it makes sense that there would be a lot of rabbits in space huh? Especially the playful ones.
A possible reason why Rosalina's storybook never mentions how she went from an ordinary little girl to an immortal goddess: if she were to write down how her ascension happened, and others got their hands on this information, someone would likely attempt to follow suit, which could have bad consequences if they fail or if the wrong kind of person gains this sort of power. Note that at the end of the storybook, she decides to visit Earth every hundred years, indicating she was already immortal by then, but deliberately left out how she got that way.
It makes a lot of sense why the bosses fought in the Garden's robust galaxies are harder rematches of earlier boss fights.
For Deep Dark Galaxy's "Sunken Ghost Ship" mission, the Ghost Ship itself looks like a boss arena similar to Kamella's personal airship. Guess who you fight on the ship itself?
To take it a step further, Kamella is a Magikoopa King Mook — so obviously, her level of dark magic is quite advanced. Deep Dark Galaxy is a haunted galaxy, and dark magic (or necromancy) is heavily involved with death. It makes perfect sense why Kamella would reappear as Deep Dark Galaxy's main boss.
Dreadnought Galaxy is basically a harder version of Battlerock Galaxy, being an advanced battle station with very similar elements as the latter (cannons, space mines, the exact same music, another secret garbage dump level, and a similar Purple Coin side scrolling level). So it should come to no surprise the Topman tribe would also overpopulate the galaxy. Guess who you fight at the end of the "Revenge of the Topman Tribe" mission?
One might assume the boss of Melty Molten Galaxy would be Tarantox, considering the bosses from the previous were rematches of those from the Fountain dome. Except, it's the Fiery Dino Piranha, self-explanatory as to who it is based off of. Not only is it a Book Ends where the last non-Grand Star boss is a harder version of the first, but it's more fitting to have a dinosaur as a boss of a lava-based galaxy — as they are more associated with volcanic environments than spiders.
It's also a Book Ends in a sense where the fight against Dino Piranha results in Mario (or Luigi) completing the first normal Power Star mission in the first robust galaxy, whereas the fight against Fiery Dino Piranha is the last normal Power Star mission in the last robust galaxy.
According to the theory of special relativity, anyone or anything traveling in space at the speed of light will cause the time around them to move slower than the time outside. If there were two people of the same age, one traveling in space and the other staying on Earth, once the spacefaring person returns from his/her journey, he/she will actually age much slower than the one on Earth, or that the latter would be long dead after the former returns. No wonder why Rosalina's an orphan.
Whenever you reclaim a Grand Star, notice how more and more Lumas will appear in the observatory grounds. Now think of how many of them were inside the observation domes when Bowser attacked — locked inside, trapped in pitch darkness all that time until the power was restored and they could escape. And these are little children we're talking about.
Keep in mind that this galaxy was just recently created by a Hungry Luma. So perhaps these two ships were minding their own business when the Luma showed up and transformed right in the spot they were in. Oops!
