Rewatching this ep, can we note how really good the animation is? Especially facial expressions and secondary animation? It's blowing my mind. Which studio did this one?
Pierrot apparently, although I did repeatedly hear rumours of studio Mir doing some help and touch-up work in a few of the first episodes, but I can't substantiate the rumour or find a source.
Occasionally Pierrot does do pretty good animation. They're just not the best with staying on-model. I love the animation of the fight scene at the end of the episode; the way Korra tries pushing herself up after the dark spirit knocked her to the ground is really well animated, and Unalaq's spiritbending is really amazing. The best animated case of spiritbending in the season I'd say.