1: Did you know that the Butcher at the start of the Depths.
This one^
Is Female?
This is an easy one, but pretty interesting. The reason why this enemy is a female is because it's a reference to the invader "Maneater Mildred". Who looks familiar to the Butcher.
And that moves us to Fun Fact #2.
2: Did you know that Maneater Mildred was a character made by the devs during test builds?
One of the Devs when testing Dark Souls made a female character that was bare naked except for the butcher bag on her head and the butcher knife. And would go through the test builds like that.
Eventually the team decided to add in Mildred as in invader in everyone's favorite area, Blighttown.
Spoiler
Maneater Mildred also ends up appearing in Dark Souls 3 as an invader.
3: Did you know that the motherfuckers called Basilisks,
Don't actually have huge yellow eyes?
Their actual face and eyes are just below the two yellow orbs.
4: Did you know that Crossbreed Priscilla actually was meant to play a different role in Dark Souls?
Hidden in the game files is different positions for Priscilla to be idle in, one of her sitting down, and a couple of her standing positions. Much like the Emerald Herald in Dark Souls 2. Priscilla was meant to be a sort of heroine character that would help the player, how is not known but most likely Priscilla would have been like the Emerald Herald or Fire Keepers.
Speaking of Priscilla, she currently resides in the Painted World, here is a fun fact on that.
5: Did you know that the Painted World was going to have another part to it?
In the area where Priscilla is standing, there is actually an area below it. Much like the Undead Asylum the floor under Priscilla was meant to break apart and have you fall below, there is even models of the floor breaking apart and being left as rubble. What would be down there is unknown but there was even models of a staircase letting you back up to the top.
As the Painted World was one of the first areas that the team worked on, it's most likely they planned on doing the Stray Demon there instead of in the Undead Asylum.
6: Did you know that far inside the Catacombs, there are caskets that you can lay in if you wish.
However that isn't the fun fact, the fun fact is that there are special animations if an invader tries to hit you inside the casket, showing them stabbing inside the casket. You can try it out with a friend if you wish.
7: Did you know that in the Gwyndolin Boss Fight, there is actually an end to the "endless hallway"? Just run past Gwyndolin and run forward for around 5 min.
And that's all I got! Do you have any? Did you learn anything? Hope you enjoyed reading!