These villains are getting less and less backstory development as we go, huh? In terms of development:
Sombra < Chrysalis < Discord / Nightmare Moon
That said, though, I enjoyed the episode quite a bit. The songs were okay, but I've only listened to them once, really. However, it was nice for Spike to get a role as Twilight's supporting vocals. Cathy Weseluck amazes me.
I did think Rainbow Dash was a bit over the top, but I enjoyed everyone else.
También, sombra = shadow en español, por tu información.