you, were Nightmare's best friend before he ate the Negative apple and became a true monster, he's covered in a black goop and has tentacles made of that goop, you know you can't save him now, but... You've decided to follow him after he killed everyone else in your guys' AU, he questions your loyalty... So he tied you up.

Nightmare enters the room that he has you locked up in, you're tied up in a cage, he approaches the cage

"So..... Give me a good reason that I shouldn't kill you too."