In Nisemonogatari, the bee of Karen Bee and the phoenix of Tsuhiki Phoenix are not really a bee and a phoenix, in keeping with the story's theme,
Bakemonogatari features Hitagi Senjogahara, a classmate of the protagonist's whose weight was stolen by a crab deity. While explaining the deity's nature, resident supernatural expert Meme Oshino mentions variant myths where the deity is instead a woman or a rabbit. The crab, rabbit, and woman are all examples of lunar pareidolia from various parts of the world. A crab/woman/rabbit that steals weight? Reduced gravity on the moon, remember?—urutapu
Hanekawa's headaches are a result of Black Hanekawa, the embodiment of Hanekawa's stress over her unrequited love for Koyomi, taking over her body; they first manifest during a conversation in which Koyomi explains why he loves Senjogahara. In retrospect, it seems so obvious. — Taelor
In the first episode, shortly after Koyomi strips Senjogahara of her various Improvised Weapons, Senjogahara says that "[her] body isn't worth committing a crime over." At first, this made no sense; on reviewing (especially with knowledge of Senjogahara's past), this remark takes on a much darker meaning. — Taelor
Similarly, the whole sequence in the second episode where she's naked or just in her underwear in front of Koyomi takes on new significance when you find out her backstory. She was probably trying to see if he would take advantage of her after what happened with the cult leader, but Koyomi passed.
After it's been made official Senjogahara tells Araragi that if anyone other than her kills him, she will kill them and die after. At first glance you might think there is no way a 45Kg teenage princess is going to beat something like a Bakeneko, however keep in mind that Araragi has a MASSIVE case of Chronic Hero Syndrome (he, Spider-man, Touma and Watanuki could form a bridge club), so much so that he will, and in fact has thrown himself to the wolves to save someone else, Senjogahara effecively gave him a will to live by virtue of not getting her hurt. — GXNext
This is further augmented by the last episode where Araragi is willing to die for Hanekawa's sake only to remember Senjogahara's threat. Only then does he actually try to fight back.
Some have pointed out that the oddities roughly line up with common psychological problems—for example, Hitagi's possession by the heavy crab, which leads to reduced weight and, according to in-universe opinion, better looks, can be easily taken as a parallel to an eating disorder.
Oshino explains during the Mayoi Snail arc that only those who don't want to go home can see and get led astray by the "snail" - Mayoi - which is why Araragi was able to spot her, reluctant as he was to deal with his family. So wait, why did Hanekawa have no problem interacting with Mayoi if- oh. Oh. Especially effective as something Araragi already would have understood about Hanekawa and not needed to comment upon, but the viewer had little to no clue about.
Not really Fridge Brilliance, more Fridge Oh-yeah-I-forgot-about-that, but it seems strange that Mayoi and Shinobu seem to be the two of the more mature girls in the cast considering they're both little girls. But then you remember that both are the oldest females on the show, one being a ghost who, should she have survived, would be in her early 20s and the other is a centuries old vampire in Sleep Mode Size. —g3m1n1
Oshino lived in an abandonedcram school. According to Shinobu, he spent his time:
"That sleazy brat spent every hour of every day filling my head with useless stories of ghosts and monsters."
He was forcing Shinobu to attend cram lessons on oddities, preparing for when he abandoned Araragi to fend for himself. —cancerlad
When Hitagi retracted the 'hiding embarrassment' from her transmutation speech in episode 1, Koyomi said she took out the most important part. Why? Because a signature character trait of 'tsundere', which she claims to be, is embarrassment. Without it, spite is, well, just spite. —lowsoman
The ending theme leads to some Fridge Heartwarming after episode twelve of Bakemonogatari. "There's Deneb, Altair, Vega." Seems like just more lyrics... until Senjogahara points them out to Koyomi on their date. Brought a smile to my face. — Ryumaru
Senjogahara is seen with a stapler in a lot, if not all, of her stills and figurines. Ever notice that it's somewhat similar to a pincer? Hello, Hitagi Crab. — Halcyon87
Another thing is that some of her figurines are seen with her holding a handful of sharp school objects. Maybe she's compensating for the lack of sharp limbs that a crab got?
Every character has characteristics that somehow symbolize the oddities they deal with/are. Like Mayoi carrying a huge back bag reminiscent of a snail's shell. And Nadeko's coat as a "second skin." Sometimes they are more internal, like Kanbaru's hobby of basketball, that involves lots of agility and jumping, reminiscent of the way of travel of monkeys. —Extablish
Kanbaru's is external, too. In Japanese, her shorts are 猿股 (sarumata); the first kanji means "monkey".
Everything we see (The art of the characters and scenery etc.) goes through Araragi, as he is our unreliable storyteller. If we see something, it may as well be something else, Araragi just saw it differently. This is probably an artistic choice the animation studio put through making most of the things said in the original book onto the screen. This can be seen in every single episode. There are no people in the background, because in the books, Araragi doesn't mention them, and thus, does not pay attention to them. Also, some scenes, like the very beginning on Bakemonogatari, where Araragi catches Senjougahara, is probably very much exaggerated by the fact that they hold deeper meaning to Araragi. — Extablish
Bit of both Fridge Horror and Fridge Brilliance all in one. In Kizumonogatari, when Hanekawa spends the New Years money that she's saved up since childhood Araragi reprimands her saying you can't replace memories. Except, given her family situation, she probably freely spends it because of the lack of feeling that's attached to the giving and receiving of the money.
The opening for Kabukimonogatari makes a lot more sense given the ending for Onimonogatari. Mayoi is wandering around the maze of signs, fulfilling her job as the Lost Cow, but she is then broken out of the maze and flies toward an ahoge, similar how she would no longer be the Lost Cow just to stay with Arararagi...Excuse me, I stuttered.
During Nisemonogatari when Araragi describes his encounter with Nadeko to Kanbaru she (jokingly) says 'you don't seem to realize who the final boss is'.Funnyhowthatturnedout...