Gideon: Hello Dipper Pines. Bet you didn't expect to see us again. The one with the one eye, and me, with the blue and the hair.
Dipper:(Gasps) Mike and Sully are back!?
Gideon: No, you idiot! It's me, Gideon, and Bill. Bill Cipher.
Bill: Its true, I'm Bill! And I have an unexpected twist to reveal about my enigmatic self. This whole time, I've had a twin brother! (shows a picture of a blue square with a bowler hat) And his name is Tad Strange!
Dipper:(pointing to Tad over his own shoulder) No, we already met Tad last week; he's just a normal guy.
Tad:(Waves)
Bill: Aw, really? Well then his name is.. the pentagram on top of Gideon's tent! (pointing at said object)
Gideon: That's really not surprising.
Bill: What, just cause Stan had a secret twin I can't too? "Long lost.. twin" That's a thing that's been around long before he has!
Gideon: It's not surprising because Ah too, have a twin brother!
Ghost Eyes: That's right! This whole time I have been (unzips Ghost Eyes costume) Gideon's twin brother, Jubilant Gleeful!
Bill: ...What?
Mabel: But did you know that I, also have a twin brother?
Dipper: Yes, Mabel, literally everyone knew that.
Mabel: I just want to be a part of things...
Bill: Go away, Shooting Star! Go find a unicorn or something!
Mabel: Okay...
Gideon: Wait, was that Mabel? Hi, Mabel! Ah love you! And might Ah just say, you're looking especially lovely today, and sounding just like Roger Rabbit!
Toby: And so you see, that guy you talked to earlier was my twin brother, Tony Determined, pretending to be me! He's such a kidder, but I've never seen you before!
Shandra Himenez: ... (walks away)
This whole thing was a paraphrase(because I can't remember all of it) of a video by PopeLickVA. it's called "A Twist About Bill Cipher." You should check it out! It's alot better with the voices and video.