Forgotten past (Billdip)

The Stan's twins were selling on a ship for 6 months and came back to the shack to see a big surprise........... Bill Cipher?
Bill Cipher is not the same. What happen to him?
Mabel is a spoiled little brat that thinks only herself is a master of manipulation, she likes using people and then throwing them away especially her favorite toy is Dipper Pines. Dipper Pines is sweet, kind, caring, super cute, and one of the smartest in Gravity Falls, he has a feminine body.

How tall they are?
Mabel is 5'4"
Dipper is 4'10"
Bill is 6'6"
Basically, everyone is taller than Dipper.

Alphas- Are rare but not as rare as an omega, can mark omegas, are dominate, and claiming them as theirs. Can let out pheromones that make omegas obey them and submit.
Beta- Can't smell pheromones, more populated aka not rare.
Omega- Have heats, tend to be stereotypically weak. Can let out pheromones when they are scared or when they feel threatened usually have blockers to make sure that they don't have any scent that Alphas can smell. Omega are the only ones that can get the ears and tail to come out in their human form. They do it whenever they want or whenever they get too scared that they pop out. When they came out it is called omega/human form.