After being defeated in weirdmeggedon, Bill Cipher didn't exactly die. He was just stripped of his most powerful powers. Basically, all he could really do was switch his physical forms and teleport. Meaning, he could no longer take over and rule another dimension. So, knowing that his first idea had been completely dissolved, he turned his attention to someone that had actually quite interested him. Dipper Pines. Out of all the humans on earth, Dipper Pines had always seemed different to Bill. Dipper Pines, regardless of how hopeless or dangerous the situation was made, he stepped up without any regrets. Thats how Dipper Pines stuck out to Bill Cipher. And now, with no more tricks, maybe this could be an opportunity for Bill to actually be a little more closer to Pine Tree.