Dipper's face speaks to me.
It says: "Mabel, stahp"

Ooh, don't go down that road, Shooting Star my 100% actual niece. I don't mean to sound like some crazy fundamentalist, but if you get too gothy, you might start worshiping demons, or getting into the dark arts an- Wait a minute…

Actually, you know what, Shooting Mabel? Forget it. You can do whatever you want in your teen years. In fact, feel free to express yourself as a goth for as long as you like! Don't make it a phase, make it last the rest of your life, and I'll make Mabeland even bigger and better, come Weirdmageddon be there to support you and your choices, all of the way through as your Grunkle.

(But seriously, make sure not to cross into emo territory, or else you might end up becoming even cringe-ier than ol' Bleeding Stitched Heart Robbie is.)