Favorite Son - S1-E6
Revealing mistake: When Lucifer is going through the forensics bag next to the dead body at the start, the body of the victim can be seen breathing. (00:07:30)
St. Lucifer - S1-E11
Revealing mistake: When Chloe is getting dressed at the start of the episode, she is wearing a flesh colored bra underneath the bed covers that she has wrapped around her when she mentions her ex dumping her by text.
Favorite Son - S1-E6
Revealing mistake: When Lucifer takes off in Chloe's car during the stakeout, tyre marks are visible in the gravel from previous takes. (00:32:10)
Lucifer, Stay. Good Devil. - S1-E2
Revealing mistake: When Jimmy grabs the cell's door, in the shot that happens before he starts banging his head on it, the supposedly secure door gives way effortlessly, showing big gaps. (00:42:30)
Revealing mistake: When Lucifer convinces Ricky not to jump off the building, it is blatantly obvious that the two actors are on a green screen and not an actual rooftop. The green glow around their heads is visible. (00:13:10)
Answer: As Cain theorises in a later episode, it's Chloe's love, not presence. This early on, Chloe had no strong feelings for Lucifer, so had no effect on his immortality. In fact even more recently he's back to being invulnerable around her after speculation that he chose to let himself be vulnerable. So while there's a degree of flexibility / retconning going on, it's all explained in-show.
Jon Sandys ★