A certain event in the Streets has Rust bring out the iron pipe to kill a blob NPC, and she continues to carry the iron pipe until you exit the area. Though the dark tint in the area makes it somewhat hard to make out, when looking closely one can see that both her attacking and walking sprites use Sabitsuki's sprites.
Sitting on any seats also changes Rust's sprites to Sabitsuki's. Both sprite bloopers get reversed if you get hit by a red demon after the change.
The special room found in the apartments has teleports coded into the game, but these teleports don't work in-game, so the only way to exit is either by using the Arm effect or waking up.
The black-haired girls all die off in the Rust chapter, except for the girl that sits in the chair in the room where one gets the Whistle effect. It's impossible to tell whether this may actually be an intentional detail or not, though.
"Bar Kaibutsu" for the Kaibutsu that can be found in the Sugar Hole on occasion.
Fans have also given names to the different Kaibutsu, most commonly "Gabe" for the bar Kaibutsu or the eye-face Kaibutsu. "James" and "Carrie" have also been used to refer to the other two Kaibutsu.
"Charlotte", for the pink-haired girl that sits by the fire in the alleyway behind the asylum.
Fan Translation: Several English ones exist for different versions of the game, and new ones come out with every new version; most can be found on the wiki here, and some others can be found on the Yume Nikki fangame wiki here.
God Never Said That: lol has never stated the gender of the Kaibutsu. The only "confirmation" of their genders is what little can be taken from their sprites, and even then, the only Kaibutsu with an unambiguous gender is the twintail model.
Wiki Rule: Found here. It is generally advised not to use the wiki, though, as it is outdated, filled with lots of inaccurate facts/trivia, and uses names for places/events/NPCs that aren't the commonly-used fan nicknames.