Even more! RD wasn't touched on as much in the video, the only things said about her being 1. she's the same grade as rarity, 2. she's short 3. she's an earth pony and 4. she's mean now.

The idea was to start her as a comical villain, described as a "Javert" type character, being authoritarian and liking rules. This struck me as a very "mean strict hall monitor" type character. She also never had a listed special "toy trait", so my idea was she changes colours in water to put the rainbow in rainbow dash, and because of her "unfinished" cutie mark and seemingly ill-fitting name, she was bullied, giving her a standoffish nature.

So, Rainbow Dash, more commonly known by just Dash, is a colour-changing earth pony, bullied for years for her goodie-two-shoes-ness and boring cutie mark. The plan is that when she discovers her magic specialty, weather magic, with her new friends, her cutie mark's design changes permanently, with her hair still only turning rainbow in water. She's tough, and kinda cynical, but really kind on the inside, wanting most to do good. I'm actually excited to think of her relationship with rarity, the two of them being the eldest of the group (aside from fluttershy, maybe?) and being in the same classes.