(I'm going to guess this is where this kind of thing goes. The Media forum and subforums claim they're for non-pony things, so...) Discuss Ask Pony Blogs ITT. My personal favorite of the moment is the Ask Loony Luna one (not linking because there's a tiny bit of NSFW-ness and it's somewhat grimdark). Also I've got my own (Ask Apple Pie) that's sorta-kinda-maybe trying to do some story-based stuff. Maybe.
The Pinkamena Diane Pie is my favourite. Then again, it's the only one I've seen. It's NSFW, just before you check it right when your dear old mother's in the room! The contrast between the bold tones and light moral messages in MLP:FiM and the murderous, sick and twisted goings on of Pinkamena delivered in a calm way really interests me. I just like it.
I just love anything by Crookedtrees. Bias aside, it is one of the best ask blogs of any fandom. It's dark, it's humorous, but it's also pretty deep and well thought out. It's interesting, I thoroughly enjoy it. I was thinking of doing a grimdark ask blog, but I don't know who would follow it so I lost interest.
I also approve of Ask Pinkamena. I'm personally rather interested in where this situation with Mrs. Cake is going to go.
