Liar, Liar, Slutty Dress on Fire - S2-E2
Revealing mistake: When the cops find the body in the hotel room, the actor playing the body is visibly breathing when he's supposed to be dead.

Starring: Lauren German, Kevin Alejandro, Tom Ellis, Lesley-Ann Brandt
Genres: Fantasy
Liar, Liar, Slutty Dress on Fire - S2-E2
Revealing mistake: When the cops find the body in the hotel room, the actor playing the body is visibly breathing when he's supposed to be dead.
What Would Lucifer Do? - S3-E4
Other mistake: When Lucifer grabs Amenidiel's phone and is supposedly typing on it, he's holding it upside down. (00:06:25)
Everything's Coming Up Lucifer - S2-E1
Lucifer Morningstar: Hello. My name is Lucifer Morningstar, and I love drugs! Love them. Mmm. Yummy, yummy, yummy. Can't get enough. And I've got lots of money. [Pulls out cash and sniffs it.] Mmmm! That I love spending on drugs.
Answer: It's Lucifer's blood from when his wings got hit by the bullets. As Lucifer spreads his wings, they're white, and before he wraps them around Chloe, you see a bullet hit his wing above his right shoulder, and the spot turns red. After that, he continues to get shot in the wings before fleeing.
Bishop73
Agreed. His wings take damage and "bleed" similar to how he bleeds when Decker is around.
Ssiscool ★
If they were normal bird's wings, the lower part where there are just feathers should neither bleed like that nor be able to stop bullets, but they are angel's wings, so they behave differently.