It would be mean of me to sugar coat it. You'll never learn anything if I just lie and say this was great.
The truth is, this was horribly random.
First, I'm not sure why you had to involve Toph in this at all. She and Korra aren't young at the same time, as a Korra fan I figured you knew that. That aside though, she didn't DO anything. She got beat up. If it was supposed to be the reason they were fighting, why did Vegeta attack Toph? Why are they in the same world? How are Korra and Toph both that age? Why is Korra in the middle of nowhere alone with Toph and Vegeta? There's a lot you didn't explain, so you might as well go all the way and just have it be "we're fighting for no reason".
Second, the audio was really really bad. The loud music both at the beginning and the end were horrible songs that had nothing to do with Korra or DB. The way the flash jumped voices was horrible and, although I practically never feel this way, in this case I think even text would have been better than the audio you used.
Third, the animation was pretty choppy and bad. No, it wasn't newgrounds fault, cause the stuff that you tweened I could still tell was moving at 30 fps, but the stuff that you did frame by frame on looked really choppy. Maybe it was BECAUSE it was right there next to 30 fps stuff. In that way I think you shot yourself in the foot.
Lastly, the icing on the cake was the end, where you used a final text screen to talk down Dragon Ball. What was the point of THAT? We could already tell you like Korra more by the way the flash went, AND your author's comments, but you had to make sure you crammed it down our throats with a closing screen of text to tell us. A little redundant.
I'll give you a star for at least attempting to animate, but this flash is a stinker.