Oh, it can be done. Easily.
3 more princesses, the CMC (great for piglets!), the Apple Family, regular recurring characters like Derpy Hooves, Doctor Whooves, Zecora, Maude Pie....
To the folks complaining about the MLP reference: last I checked, you don't have to paint them the way they are shown, right? Want them spookier, pale horses with black or fiery manes. Want something gross? Rotted green ponies with grey, dirty manes... Spectral ponies? Bone white with a nice blue or green wash.
No one is holding a weapon to you making you paint them cutesy.
Let those of us who want to do so in peace, please.