The Mission

Bill Cipher is the son of a wealthy genius with a lot of enemies. Dipper and Mabel Pines are two of the best assassins in the business. Dipper lives off one rule. Don't let your emotions sabotage the mission. But what happens when he is assigned to kill the man he falls in love with?

(The assassin idea is from NicholeR0429, but everything else is mine)
(Gravity Falls belongs to Alex Hirsch and Disney)
(Art and pictures are not mine unless I say they are)