The pitch video has IGA calmly explaining his goals and plans for Bloodstained, much like a normal Kickstarter pitch video. And then there's a random part where he tortures a man for no reason. Doesn't really make much sense... until you realize it's a Visual Pun. The man IGA tortures is strapped to a rack, a torture device that stretches the victim apart. And IGA is doing this while talking about the project's stretch goals.
Before Gebel was afflicted by the magi-crystal curse, he was seen wearing glasses. But after the curse has affected him to such a degree that it practically covers him everywhere, he's not wearing them anymore. What if the crystals over his eyes double as a lens that adjust his sight to work perfectly?
Another bit of Fridge Brilliance is how well Bloodstained and Castlevania line up in terms of origins. First off, what do we know that is the reason that Leon gains the ability to use magic and has upgraded his whip into the Vampire Killer? What is the reason that the Ebony and Crimson Stones exist, the latter of which Matthias used to forsake his humanity and become a Vampire/Dracula? The answer is simple: Alchemy. It's the reason that the problems (as well as the solutions) are present in the Castlevania universe, and now it's the same thing in the Bloodstained universe! Not to mention it's the only type of magic not used by any player characters in Castlevania, whereas here it's now at the forefront.
As mentioned on the main page, the path to the Golden Ending requires actions that seem like Sequence Breaking while not being hinted at in-game. It's obtuse by modern game design standards, but it's possible to stumble onto on your own, especially if you're obsessively searching every corner of the map for secrets or a Disc-One Nuke as were so common in Iga's previous titles. In other words, getting to the true end of this Genre Throwback is a reward for knowing what to expect of an Igavania title.
Indeed, getting better endings in past games of IGA's often required a lot of inventive exploration and ability use.
There's also a story justification to why these are bad endings. The Just a Flicker ending has Gebel killed before the revelation that Dominique is Evil All Along, so she can carry out her plans while Miriam and Johannes are unaware that she's doing something far worse, while the Usurper ending presumably has the hidden Gremory eventually corrupt Miriam the same as she did Gebel.
The language of flowers is actually pretty fitting when one considers the meaning of Roses, their colors and how they apply to the three sharded characters in game.
The combination of roses and blue hues as motifs for Miriam make sense on an individual level. But when taken together (particularly in her best sword, the Blue Rose), they become even more meaningful. Since roses do not naturally produce any variety of blue pigment, it's impossible either through chance or horticulture to produce an actual blue rose. Doing so requires experimentation and alteration of the base nature of a rose itself. Just like a blue rose, Miriam is the result of humanity's experimentation and modification to make what would otherwise be impossible. Likewise, in the language of flowers blue roses symbolize "mystery", "longing to attain the impossible", and even believing those who have blue roses "Will have their wishes granted". Miriam is trying to find out the mystery behind Gebel's FaceHeel Turn, she wants to save him, but he dies no matter what, making her attempt to let him live impossible, but she still gets her wish in that Gremory's control finally lapses and lets Gebel be himself before he dies, thus "saving" him.
Gebel's motif is obviously red roses, given how far the crystallization curse has spread throughout his body make his whole body appear as if they're covered by them. It fits in the sense of Red and Black and Evil All Over, given how he wants to wreck the world for what the Alchemist's Guild has done to him and Miriam. However, red roses also serve as symbols of love and devotion, which fit for Gebel as he also wishes to include Miriam into his plans. Symbolically, they can also mean deep regret and sorrow, which befits how Gebel dies no matter what happens.
Dominique is the last person we see having the shards bound to her body. Her color is overall the same as Gebel's, being a blood red. However, her version of red roses instead points towards the idea of them serving as revolutionary symbols, such as how Socialists and Social Democrats in the later 1800s and early 1900s have used it as a symbol for their parties. Given that Dominique wants to use the power of the crystals to essentially tear Heaven and God down, it certainly fits in the style of the red rose symbolizing politics and revolutionary ideas. It could also be seen as how she subverts the meaning of the Red Rose referring to true love, due to how she uses everyone around her. Going on a bit of a stretch, one could even say that if we take her hair color into account, she could accurately depict yellow roses. In the language of flowers, they can symbolize platonic relationships, jealousy, and are even used in farewells, which befits how Dominique befriends people in order to use them, is envious of the demons' power and wishes to use it for herself, and how she inevitably leaves to betray everyone else.
For a non-character example, the presence of lavender flowers is a perfect fit for save rooms, as they represent healing (the save room heals you to full), silence (music cuts off inside one of them) and relief (which a player is sure to feel when reaching one at low health).
In the Den of Behemoths, right before you fight Valefar, you'll more than likely have come across some blue chests that only contain money and not useful materials for alchemy. Now, this might seem odd, especially given a chest you can find right beneath his own stage where his feet is. Shouldn't he be greedily keeping this to himself...? The Fridge Brilliance kicks in in that he explicitly wants you to pick up the money laid out for you. When you face him and kill him the first time, he uses a move where he restores his health equal to how much money you have, and you'll more than likely have enough to replenish his health and then some if you have much more than what you entered the Den with! Those chests full of money are more or less literal life insurance for Valefar!
Plenty of the Demon's placements or what they affect in story in Ritual makes sense when one reads what they affect in the Ars Goetia.
Vepar is said to govern the waters and guides armored ships laden with ammunition and weapons. She's the one who makes the Galleon Minerva crash into Arantville as Gebel wants Miriam there.
Andrealphus is said to teach cunning in astronomy and teaches geometry in a perfect manner. What better place for a demon who teaches such things than the Livre Ex Machina, aka the Library?
Valac is said to appear as a poor boy with angel wings riding a two-headed dragon, and gives true answers about hidden treasures. The former befits how he's at the towers that reach up to the heavens. The latter is true because using Invert or High Jump at his boss arena is where you can find the Aegis Plate, one of the things necessary to reach the Oriental Sorcery Lab that can lead to the better ending.
Bathin is said to know the virtues of precious stones and herbs. What better place to be than at the Underground Sorcery Lab, one of the Alchemist's Guilds headquarters that requires previous things to do their work?
Orobas is said to grant true answers of things from the past, present and future of come. It's from making use of his Invert shard that you can gain access to the Oriental Sorcery Lab, which can set you onto the true ending of the game.
Valefar is said to be a good friend of thieves and a good familiar by his associates until they're "caught in the trap". He comes right after learning that Dominique is hiding secrets and more than likely betrayed you. She also got Gremory to steal the Liber Logaeth back from Alfred, befitting the "thieves" part.
Some Fridge Horror laden with Nightmare Fuel. In the Bael fight, you can hit any of the heads you want to hit, but if it's not one of the ones that Dominique is on, then it'll only put that head out of commission for a short time. Which begs the question of: What if Dominique wasn't there as a weak point for Bael? Without her acting as the anchor for him, and if he wasn't truly killed by having all of his heads put down at once, would it not make him completely unstoppable? If the Alchemists Guild doing a botched summoning led to 10 years of destruction by demons, then if their summoning were truly completed, it would become a literal Hell on Earth because nothing humanity could throw at Bael would truly work!
Dominique and Gebel are arguably dark reflections of the Belmont clan in the Castlevania series. Their exorcist bloodline allows them to resist demonic power, yet rather than becoming heroes because of this, Gebel becomes a test subject for the alchemists and the possessed pawn of a demon (something he seemingly doesn't survive) and Dominique goes off the deep end after seeing her family destroyed and resolves to gain demonic power for herself, showing what could happen if a Belmont willingly turned bad and combined their strength with demonic might. Dominique even uses a whip and light element attacks to reinforce the parallel further.