It's not arbitrary that the stairs to the throne room have crumbled. Richter and Maria treat physics like a mere suggestion with their martial arts, and Alucard can access them via embracing his vampiric powers.
When fighting the 3 doppelgangers in the Reverse Colosseum, Alucard is oddly absent. Until you realize that you've already fought an Alucard doppelganger, which serves as two separate boss battles in other areas.
Another two factors also possibly exist for why Alucard's hair changes.
The first is genetics: Dracula has been shown to have black or white hair at different times in the games and possibly depending on his reincarnation status, not to mention he did have black hair as Matthias. Alucard likely did initially have black hair, but it turned white as he grew older, akin to how kids hair colors can change as they grow up.
The second idea however is stress: having too much of it can turn your hair white, and let's take a gander at Alucard's life: hes seen his mother die and had to fight against his own father to stop his rampages, with his first go at it in Dracula's Curse having the text mention his guilt and Symphony of the Night taking place 300 years after the fact, the whole time Alucard spent asleep. What if he couldn't deal with the trauma and chose to seal himself away as way instead? All the endings in the game also imply this as he feels he's an unclean thing who shouldn't live alongside humanity. Hence, he's heavily traumatized and filled with stress due to the circumstances he's had to deal with and will deal with in the future. Perhaps the reason he goes back to black hair as Arikado is also because he can be at peace knowing his father is finally and unequivocally dead and has a better chance at life as Soma Cruz.
Kind of a minor detail, but still something interesting to note. When going through the Catacombs, you eventually get to a section where there's fire and lava around on the floor. But in the Reverse Catacombs, the same area is instead shrouded in ice. Why is this? The deeper into the earth's crust you get, the warmer it is and the higher in the sky you get, the colder it is. The normal Catacombs are underground the castle, whereas the Reverse Catacombs are very high in the sky in the Reverse Castle.
It may sound cheesy to have Dracula quoting the Bible at the end of the game once he's beaten again by Alucard, but it actually makes sense when you think about it. Recall that before his vampirism with the Crimson Stone and Walter's soul, he was Mathias Cronqvist, a knight for the Church. In a way, however you may look at it, the quote makes this scene even more somber and a bit of a Tearjerker even since Dracula seems to be not only opening his eyes to his folly, but remembering his roots in a way and what he's ultimately given up and lost for nothing.
The music for the Alchemy Laboratory area is called "Dance of Gold". A common practice among alchemists was the search of a chemical formula capable of transmuting base metals into gold.
In the PSP version, when you look up the Frozen Half enemy in the enemy encyclopaedia, there's a note saying they're transsexual. At first, you might think that that's a weird thing to work into designing an enemy... then you think about the genre the Castlevania games take their inspiration from, and you realise that you are fighting sweet transvestites from transsexual Transylvania.
Regardless of the translation your playing, this is the first time that Dracula calls out to something to power him up. In the PS1, he calls out "Playtime's over! Grant me power!", while the PSP version goes for "Enough of this! Give me power!" While it may seem like him calling to Satan to power him up might seem like it makes him look weaker, he isn't calling out to the Prince of Darkness, but rather calling out to Chaos itself, of which the Castle is a creature of. In a way, Dracula is foreshadowing the fact that his power is tied to the castle, in turn allowing him to be Hoist by His Own Petard in 1999.
When you think about it, the Inverted Castle is more than just padding: Dracula is a vampire. Vampires are associated with bats. And what do bats like to do? Hang upside-down!
Let's look at the bad ending of the game. Richter is killed and afterwards, Alucard leaves the crumbled castle to return to his slumber. But Shaft is still alive and will go through with the resurrection of Dracula in the reverse castle. With the Belmont Clan dead, and Alucard nowhere to be seen, that leaves no one able to stop this disaster.
Worse still, there's two variations of this ending, depending on whether Alucard received the Holy Glasses from Maria in the center of the castle or not. If he did receive the Holy Glasses, then the dialogue that follows sees him filled with self doubt on what he'd done, while Maria can do little more than lament on Richter's fate, vowing never to stop looking for the source of his madness. If Alucard did not receive the Holy Glasses, however, Maria doesn't even appear outside of the castle. Considering that Castlevania itself was just seen being destroyed, even in both variations of the bad ending... what are the chances that Maria's disappearance in the variation of the bad ending that didn't see Alucard receiving the Holy Glasses is because she was unable to escape before the resulting collapse?
If you use the priest side of the confessional booth in the chapel, the female ghost that sits down and weepingly pours her heart does so endlessly until you decide to stand from your seat. Just how much has this woman sinned in her mortal form?
