fasigonio

Maybe it's actually that it's archaic and, therefore, used only for grandiose things? Serial killers are usually given "cool" names.

I don't know exactly what the connotation is, but it's real.

"Slay" is a funny word. I think of it mostly having a connotation of a just person killing something evil. So I could slay a dragon, but not a chicken.

It has connotations of heroism.