Poison Ivy and other villains sometimes go on killing sprees, but they will still spare people they like. Except Joker. He’ll kill anyone.
Warning! Spoilers ahead for Poison Ivy #3
Poison Ivy is currently on a mission to take revenge on humanity. She is letting the murderous criminal inside take over and has plotted to infect as many people as she can with a deadly fungal spore. Without the strong connection to the Earth’s Green that she is used to, Poison Ivy is left weaker and has grown bitter because of it. She wants to isolate herself to keep a low profile and only emerge to spread the fungus as much as possible before it claims her as a victim.
In Poison Ivy #3 by G. Willow Wilson and Marcio Takara, Ivy is lured out of hiding by her landlord who offers to knock some money off of her bills if Ivy helps clean up a courtyard the landlord hopes to turn into a garden. Surprisingly, Ivy has a great time helping her out. She enjoys being in the sun and planting new trees that eventually blossom in the courtyard well beyond the landlord’s expectations. But Ivy eventually freaks out when the landlord tries to touch her because then she will undoubtedly become infected with the fungus.
Ivy admits in this moment that she has grown fond of the landlord and doesn’t want her to die. This directly contradicts her previous intentions, which is to kill as many people as possible. It also falls in line with many other of Batman’s villains. They are cold-hearted killers, but they are also not immune to growing fond of individuals and forming friendships. The only Batman villain that this undoubtedly doesn’t apply to is the Joker, who will kill anyone and anything regardless of his relationship with them.
Joker is seen as the physical embodiment of anarchy and chaos. This means that there are no rules that apply to him and he can pretty much can do anything at any time. Even Harley Quinn, who he views as his ride or die companion, wasn’t immune to his abuse. So it doesn’t matter how friendly Joker’s henchmen become with him. He would kill them at the drop of a hat simply because he wanted to and enjoys it. This makes him Gotham’s ultimate villain, and, ironically, the only person he wouldn’t kill is Batman because he obsesses over their relationship so much even though they are arch-enemies.
So given that Poison Ivy can show how even villains can spare lives because of friendship, it also reveals that Joker can take lives because of a friendship too.