This is how Nightmare Nova reveals to Nyx she is her mother goes in My Little Pony Transformers: The Empire Strikes Back.
[We see the battle between Nyx and Nightmare Nova still going on]
[Nightmare Nova then corners Nyx]
Nightmare Nova: There is no escape. Don't make me destroy you.
[They continue battling until Nightmare Nova cuts off Nyx's horn]
Nightmare Nova: Nyx, you do not yet realize your importance. You've only begun to discover your power! Join me, and I will complete your training! With our combined strength, we can end this destructive conflict, and bring order to the galaxy!
Nyx Sparkle: I'll never join you!
Nightmare Nova: If only you knew the power of the Dark Side. Ryan never told you what happened to your mother.
Nyx Sparkle: He told me enough! He told me you killed her!
Nightmare Nova: No. I am your mother.
[Nyx is extremely shocked]
Nyx Sparkle: No. No. That's not true. That's impossible!
Nightmare Nova: Search your feelings, you know it be true.
Nyx Sparkle: Nooooooo! Noooooooo!!!
[Nyx puts her head in her hooves as she cries]
Nightmare Nova: Nyx, you can destroy Nightmare Moon. She has forseen this. It is your destiny. Join me, and together, we can rule the galaxy as mother and daughter.
[Nyx thinks for a moment]
[She looks down and sees how far down the drop is]
Nightmare Nova: Come with me. It is the only way.