I am standing in the middle of the room. Sweetie Belle enters and calls my name over and over again. I try to tell her I'm right here, but I can't open my mouth. The room fades into white while Sweetie Belle turns into Discord. I nearly gag.
Discord laughs at my expression and snaps his paws. Were floating over a volcano. I scream and try to run to the edge for safety but can't move. I hear his laugh again, then a snap, then we're over a shark tank. I try to run away but I can't. His laugh echos in my ears, one horrifying scene after the next. We're finally back in the white room.
"Why did you torment me so?" I ask him angrily. He raises his eyebrow and holds up a squirming Sweetie Belle. I gasp, horrified at what he'd possibly do to her. He snaps his claws. She stops moving.
She stops breathing.
"You monster!" I cry.
He laughs, as if this were all a joke. "Next time, Rarity," he says, "be a little more kinder to me." He leans in, boops my nose as if this were all a game. "And I will stay out of your head."
Twi's Notes
I can't tell if the Discord in that dream is real or not. The death of Sweetie Belle means that Rarity is reluctant to let her grow up and become her own mare, while Discord killing her shows Rarity hardly trusts him.
Did he do something to her to make her despise him so? I mean, I don't like him that much, but I've never dreamt of him killing anypony!