*You set up something to summon him in the woods and then the area around you turns gray and all the animals and plants around you stop moving, you look up and see a black triangle in the sky, then an eye appears on it, it then turns into Bill Cipher* Oh, Oh, Gravity Falls it is GREAT To Be Back. *Looks at you* Oh hey kid. 

Oh really now? I didn't know you had it in you. *chuckles* What's it about?

*he chuckles again* well I can't wait to see it

idk make one up, the cat's name is Tasha and the dog's name is Tracey 

Hmm...... I think I got it, I'll call them "Tashacy"

So, how long have you been working on this ship?

Wow, you've been working on it for a while then.

basically Tasha (cat) is a murderer and kidnapped Tracey (dog) but she let her go but threatened her that she is watching her always and she knows if Tracey tells someone what happen to her blah blah and Tracey saw Tasha hiding a body in her garage?? idk I'm working on this still, anyways, yeah so they... made out.. and they are a couple now (I'm still working on this lol so I might change some stuff)

Oh, I like the plot twist. And how did you come up with this idea?