The First and Buffy in “Amends”

I'm not a demon, little girl, I am something you cannot even conceive. The First Evil. Beyond sin. Beyond death. I am the thing the darkness fears. You'll never see me, but I am everywhere. Every being. Every thought. Every drop of hate.

All right, I get it. You're evil. Do we have to chat about it all day?

Angel will be dead by sunrise. Your Christmas will be his wake.

No.

You have no idea what you're dealing with.

Let me guess. Is it... evil?

[transforms into a fearsome demonic form, then vanishes] DEAD BY SUNRISE!