What happens if you kill one? I read somewhere if you kill a unicorn you will be cursed as they are the purest creatures in the world. Is this true?
It’s more complicated than that, but in short, yes.
Unicorns are considered sacred creatures. Like you said, they’re considered the purest creatures in the world. To kill one is very disgraceful to everyone around you and you would be considered a being of pure hatred and evil. But a curse? No. Curses are much different.