After I posted my fan art of Dipper Pines and Cat, I finally give you their siblings, Mabel and Dog! I listed reasons why Dipper and Cat would be compatible with each other, and now I give you reasons why Mabel and Dog would be compatible with each other:
1) They're both the more happy-go-lucky siblings
2) They both often tease their siblings, the way siblings do (Dipper and Cat)
3) They both try to see the upside of everything
4) They both have big hearts
Anyway, I posed them taking a selfie together while "being cute and great" (to quote Mabel Pines).
Mabel Pines (c) Disney/Gravity Falls
Dog (c) Nickelodeon/CatDog