If Vayne stumbled upon Amumu, would she kill him like any other demon? It's kind of her MO that all demons must die, regardless of their intent, and Amumu is harboring a demonic curse. https://art-of-lol.com/wp-content/uploads/2017/12/amumu_wallpapers_League_Of_Legends_5.jpg
It's Amumu, he's never going to have a friend. Also, Vayne killed a mother figure to her upon discovering she could shape shift. I don't think she'd show any sympathy.
Ofc she'll do.
Vayne's short story has her note that it's more fun when her enemies are crying/heartbroken.
: "...... Well that was almost too easy to be fun. Almost."
She'd definitely kill Amumu. After all she killed her mother figure without hesitation the moment she knew that said mother figure was using dark magic.
Vayne sees the world in a black and white morality and if you are using "dark" magic,then you are evil in her eyes,regardless if you use this magic willingly or not.
