Here is how Princess Yuna and her cousins begin their fight against the Nightmare Family and Bill Cipher in Genesis World.
Later, The Nightmare Family and Bill Cipher are about to take over Genesis World. But, They still don't have the Journals yet.
King Sombra: At last. Genesis World is ours now!
Bill Cipher: We'll grab hold of the Journals yet! (in his normal and demonic voice) And we'll rule all of Equestria!
Princess Yuna: Not today, Bill!
At last, Yuna and the other young alicorns came just in time.
Bill Cipher: Oh, Come on!
Nightmare Moon: Princess Yuna!
Nightmare Rarity: And her pitiful cousins!
Princess Flurry Heart: Looking for these books? (showing the Journals)
Bill Cipher: The Journals, Give them here!
Yuna was making ready to take down Bill. But, Nightmare Trix got in her way.
Princess Yuna: Nightmare Trix!
Nightmare Trix: (blasts Yuna) Take that, Princess!
Nyx: Hey! No Pony does this to my cousin!
Princess Jubilee: It's over!
They kept on fighting the Nightmare Family, But Nightmare Moon got Yuna covered.
Nightmare Moon: All of you stand down while you still can! Just give us the Journals or death will come, And all you love shall suffer. Now, Give us the 13 Journals!
Princess Yuna: NEVER!
Nightmare Moon: Fine!
Bill Cipher: (in his very deep demonic voice) Say "Bye Bye", (change his size) Princess Yuna!
As Nightmare Moon and Bill prepares to fire, A loud roar came.
Cerberus the Nightmare Train: The T-Rex!
Princess Yuna: Good girl, Heather. (pets her) Good girl.
Yuna opens the portal to Tartarus and sucked the Nightmare Family and Bill Cipher for good.
Princess Twila: Say hello to Aku, Tirek and Cerberus.
The Nightmare Family: NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!
Bill Cipher: NOT AGAAAAAAAAAAAAAAAAIIIIIIIIIIIIIIIIIIIIN!!!
The Nightmare Family and Bill are back in Tartarus.
Princess Yuna: That takes care of them.
Princess Skyla: What about the Piranhaconda?
Princess Twila: We gotta get rid of it once and for all.
Princess Flurry Heart: Otherwise, It'll be too late to stop it now.
Princess Yuna: And we will. Come on!
Yuna and her cousins begin searching for the Piranhaconda.