It seems that Nickelodeon wasn’t quite ready to release the trailer for the upcoming season of Legend of Korra, but someone forced their hand. Co-creator Bryan Koneitzko explained on his Tumblr that, “Thanks to the shenanigans of Leaky McLeakerpants, we have released the *OFFICIAL* Book 3 trailer early.” This is why the trailer has no voice work or sound effects, but with this level of animation you’d hardly miss it.
I will say now, if you don’t want to see what characters are showing up/coming back you might not want to watch. And probably just throw your computer away because you’re not going to be able avoid this.
Zuko’s back!