What happens next?

She's mute when she's angry

"Er, how did you do that?" asked future Amy as she noticed the way naked Buffy suddenly lost her ability to speak after Dark Buffy made a magical gesture in her direction. "You're not a witch. And er, why did you do that? After all, Buffy is your past self."

"So she claims," said the black-clad figure who called herself Dark Buffy. "As for how, your old friend Vengeance Angel Amy taught me that trick. Apparently you don't have to be a witch's daughter to cast a spell if you practice enough."

"Do tell," said Willow. "I mean, how horrible -- for Buffy, of course. You are going to reverse it, right?"

"What fun would that be?" asked Dark Buffy.

"Don't bother begging her to reverse it, Willow," asked Faith. "I can make her reverse it. All I have to do is say the words, 'I wish that --'"

"Shut up, Faith," said Dark Buffy as she once again made the same magical gesture that she had used on Buffy.

And then suddenly Faith no longer had the ability to speak.

"I take it that the rest of you don't need to be reminded of the foolishness of trying to make a wish that reverses that, right?" asked Dark Buffy.

As the Scoobies nodded, future Amy gestured to present Amy, who nodded in response and started to mutter a transformation spell under her breath.

But before it could be completed, Dark Buffy turned toward present Amy and said, "The first witch who tries to cast a spell on me loses an arm. The second loses a leg. Try anything after that and you'll lose your head. Any questions?"

Present Amy stopped chanting and put her arms down.

"Good," said Dark Buffy. "Now we understand each other. Personally, I don't see why you two would want to oppose me anyway. I have all the abilities of a Vengeance Angel plus Slayer strength. You'd have to be a crazy person to think that you can take me on."

And of course, it was at that moment that Faith Lehane chose to pounce on Dark Buffy.