This is Coalmine Canary, an expert engineer and Wonderstruck's mentor. She's an older mare, and inhaling coal dust for decades has left her sounding a bit like a talking garbage disposal, but she's still got a lot of pep in her step and doesn't plan on retiring any time soon. She loves getting her hooves dirty, and it's pretty rare to see her not covered in soot.
She's also quite the lady's mare— despite her rough exterior, she has a way of charming even the most hoity toity of mares, and has quite the romantic history behind her. These relationships rarely last, though. She claims it's because she's always traveling with her work, but she's probably just afraid of commitment.