Nightmare Ark is the dark counterpart of Invader Ark.
Nightmare Ark was born at the same time as Invader Ark. When her PAK was installed, she was filled with a darkness and power that none of the other Nightmare Irkens had ever felt. She wanted to take over the Nightmare Dimension, but Nightmare Tak stood in her way. She planned to kill Nightmare Tak, but when she tried the first time she was caught and became an outcast.
Nightmare Ark saw her counterpart, Invader Ark, when they were seven Irken years old. She automatically desired to destroy Ark, but knew if she did she would destroy herself, and left her alone.
Nightmare Ark is incredibly evil and is one of the scariest things in the known universe. She is cruel to everyone and everything, and abuses her telekenesis.
Nightmare Ark looks exactly like Invader Ark, except she has dark gray skin, black eyes, and black clothes.
Nightmare Ark hates everyone. Case closed.
Nightmare Ark has never seen the sun, which she is perfectly fine with.
The part of the Nightmare Dimension Nightmare Ark lives in is so dark that when she leaves it she has to cover all of her skin to protect it from the light.
"Your smile is making me sick."
"Yes, I hate you. Isn't that obvious?"
"You may be ruler of this world, but you don't scare me."
"Come with me, Ark. Walk into the darkness. We both know you want to..."
"You're as pathetic as your counterpart."