Aziraphale and Crowley wear white and black, respectively, which is a subtle nod to them being an angel and devil, respectively. This is also a subtle nod to Yin and Yang, from the Talmud, which fortells of Ragnarok, the anglicized version of Yom al Ayama, which—spoiler alert—is what the story is about.
Mar-Vell’s cat is a crossover from Lovecraft’s universe of Elder Gods. In fact, Goose is an anagram of Cthulhu, which is a subtle nod to my inability to spell and ignorance of what, exactly, an anagram is.
When it rains, some members of the rag-tag group of superheroes use umbrellas to keep dry. This is a subtle nod to the eponymous series title, Umbrella Academy.
When the school nurse has to cut Gwen’s hair to free her from Miles, the hair left on Miles’ palm is a subtle nod to his pubescent pursuit of the masturbatory arts.