Here there be spoilers...
In the final episode of season 2, "Light in the Dark" Tenzin urges Korra to connect with her own spirit in order to defeat Unalaq. While meditating in the Tree of Time, she manages to tap into the energy of the universe and astrally projects herself, instigating a fight with Unalaq at Republic City. (this description comes from the Avatar wiki, so I don't use it as a definitive resource in this case...unless it happens to be right...)
What was that power she used to battle the fused Unalaq?
- Was it energy-bending?
- Was she harnessing the power of the harmonic convergence?
- Was it more powerful than her normal Avatar state or merely different?
As a bonus question: Did Unalaq/Vaatu seem significantly more powerful than Korra/Raava or was it all in my mind?