(You're playing as Dream Sans)

Nightmare: My, my, Dream... How horrible and neglectful of a brother you have been to allow such a thing to happen to your little brother here. Not to mention, you failed to save him when he was right within your reach… you miserable FAILURE.

He says to you upon his awakening

The fight had begun, your choices are: FIGHT, ACT, RUN, CALL FOR HELP