Ask Pony blogs

Likely due to the ease of customization and image posting on Tumblr, the blog host has become the home of a staggering number of art blogs starring ponies. Multiple blogs exist for nearly every major, minor, and even one-shot character in My Little Pony Friendship is Magic, some of which attempt to stay true to their canon personalities, and more that reinvent the characters in several ways, including pirates, stoners, offensive psychos, and ridiculously cute blobs.

The most active of the Ask Blogs acknowledge the multiplicity of Twilights, Pinkies, Trixies, Celestias, and so forth in their "multiverse," and while each blog is mostly a self-contained world there are occasional crossovers. The largest cross-over to date may likely be when Rainbow from the Ask Pony Blobs tumblr was shot out of a cannon and went flying through numerous other blogs, to their resident's confusion and occasional misfortune.

Art styles vary as much as the theme and content of the blogs, ranging from show-accurate vectors to monochromatic sketches to colored pencil.

Equestria Daily once made a request for Ask Pony blog link submissions and was swamped within minutes of the announcement, evidencing the sheer volume of blogs that exist out there. Sethisto has since resorted to occasionally spotlighting particularly popular blogs rather than making compilation posts.

Twilight Sparkle

 * There was a big crossover between the Friendly, Paranoid, and Sketchy Twilight blogs listed above.

Original mane six
(Does not include Applejack, as she actually made it into the current mane six, unless the Tumblr specifically says it's about G1 Applejack)