Earth pony time!
 
So, like the other pony races, earth ponies have many variations, even without interbreeding between the races. A pure earth pony tends to be very strong regardless of what they look like, however. Earth ponies don’t have obvious outward magic, but instead it’s spread throughout their bodies, with more in the hooves. Earth ponies use earth magic, which can have a lot of variation- from making things grow to crushing things! They also have more dexterity than the other races- what a unicorn has to do with magic, for example (say, weaving or sewing), an earth pony can do with her hooves. Their hooves are big and much harder than pegasi or unicorn hooves.
 
When bred with a unicorn, an earth pony becomes less strong, but her magic may become more articulated. Bred with a pegasus, they retain their speed and strength, but also become less potent with earth magic, although they may gain some air magic.
 
Applejack is a pure earth pony, and it shows. Her earth magic is very strong. She’s based off a clydesdale, and even if she wasn’t always working on the farm, she’d still have muscles.
 
Pinkie, on the other hand, is part pegasus- her grandmother Surprise shows very heavily in her. It’s part of why she’s so fluffy- her fur is much more like down than like fur. She also has a grasp of air magic- although it expresses itself through her body instead of through wings.