Genius Bonus / Fiend Folio

Despite being a Denser and Wackier The Binding of Isaac Game Mod, Fiend Folio has some incredibly interesting origins for some of its content.

• One of the poses Venus can take◊ is a reference to Austin Osman Spare's "The Death Posture".
  • Two of the room layouts in the Cacophobia fight are named "CLOTH MOTHER" and "WIRE MOTHER", referencing Harry Harlow's studies on mother-infant bonding through monkeys and fake surrogate mothers. Fitting the results of the initial experiments (where the wire surrogate mothers were considered undesirable compared to the cloth surrogate mothers), CLOTH MOTHER provides an easy path to shooting Venus, while WIRE MOTHER constricts the path of the former with extra eyes and thus making it inherently undesirable when CLOTH MOTHER exists.
• The enemies Tommy and Benny are tumor-like spiders, one spawning the other, and were originally named Malignant and Benign, referencing the behavior of their respective tumors.
• Lipomas are a Lump variant found in Scarred Womb, and in real life they are a type of common, harmless tumor found in the adipose tissue below the skin.
• The Alfil, a Bishop variant added in the 2.7 update, is based off of the fairy chess piece of the same name, which can leap two tiles away in diagonal. It was a predecessor to the Bishop, and was used in its place in standard chess before the 16th century.
• Stolas are owl-like enemies found in the Mausoleum, which are based on Stolas, an owl-like demon with long legs that teaches astronomy to its summoners, reflecting his constellation-like attack.
• Zissuru is a support enemy that creates a ring of salt around itself that protects enemies inside the circle. It is named after a Mesopotamian ritual that is identical to its attack, albeit with flour instead of salt.
• The Apega is named after a torture device similar to an iron maiden used in Ancient Greece.
• The Marzlammer is a Slammer variant in the Corpse that spawns maggots with each slam. It references casu marzu, a cheese known for containing live maggots.
• The Whale and Whale Guts enemies are a reference to a real phenomenon where a decomposing beached whale can build up huge amounts of gas that, if not released, will cause the corpse's guts to explode out.