Mabel's actually pretty good with electronics if she could consistently and effectively rig her clothes to light up AND play sound.
Mabel from the intro song, wearing a sweater that lights up as long as she plugs it in. It also has a switch. This indicates thats she's using simple LED lights and circuit board, tho it wouldn't be surprising if she's using an arduino kit too.
The boom box sweater from s2x01 Scary-oke is the most impressive. Not only does it light up when touched, it also plays a sound! It reminds me of those greeting cards that play a song when you push into it. However, Mabel's is way more complicated coz of the LED lights + mini speaker. This also has batteries. It's an improvement to the sweater that needed to be plugged in.
The lightbulb sweater in s2x02 Into The Bunker is a variation of the BoomBox sweater. It also lights up when pressed and runs on batteries.
And ofc, how could we forget the impressive Sock Opera from s2x04. It's a whole complicated puppet production with music, lights, special effects.
.....
I imagine that aside from knitting and art supplies, Mabel also brought a whole ass electronics kit (with arduino boards and many LED lights) from California to play with.
Knitting different sweaters everyday was already impressive enough (knitting also involves quite a lot of math and 3d visualization); adding electronics features and making them interactive is just a whole upper level of ability. I won't even be surprised if she's etching the circuit boards in the bathtub (coz i dont think she'd be content if the final product was on a breadboard). It's easy to imagine Mabel soldering the components on the dining tabe and doing some programming to get the LEDs and amplifiers/speakers to light up and sound in any way she wanted, all the while Dipper is busy with perusing the journals or practicing some advance math..
Most futurefics put her in Arts and Design careers but heck, Mabel will actually do pretty damn well in STEM if she wants to. She has already got the technical and applied experience from making her electronic sweaters.
She's really quite similar to Stanley Pines and Fiddleford Mcgucket. They're all good at dancing/moving their bodies to music, they're hella creative and they're damn good at practical electronics and machinery while still remaining whimsical and silly.
