Ok, so I watched the Avatar origin episodes...
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I thought it was going to be a letdown, but it was alright. Not great, but I mostly liked everything about it. Except for the dark spirit part. It reminded me of Samurai Jack.
Long ago in a distant land, I, Vaatu, the shape-shifting Master of Darkness, unleashed an unspeakable evil! But a foolish human warrior who mastered the four elements stepped forth to oppose me. Before the final blow was struck, I tore open a portal in time and flung him into the future, where my evil is law! Now the fool seeks to return to the past, and undo the future that is Avatar: The Legend Of Korra!
Unsure whether it was desire or despair that kept me drawing breath. When all my dreams came down to nothing, left me just another piece of meat. For you I carried my life on in my teeth. Through betrayed years and bloody tears, and pits where you can only crawl. Poor Grendel's had an accident... So may you all.