Through out the new series The Legend of Korra. Avatar Korra has many flashbacks of Avatar Aang. You see that when Korra has a flashback it is always involving Avatar Aang in 128 AG also it seems that she is always getting knocked out by somebody. In the first flashback, Amon knocks her out. In the second flashback, she is being knocked out by lightning. In the third Councilmen Tarrlok is knocking her out. At a trial for Yokone, it is not clear yet what the reason for this trial is. As stated by Councilmen Tarrlok In the beginning of episode four "The Voice In The Night". " Think back, 42 years ago Republic City was threated by another dangerous man Yokone. Your father wasn't afraid to deal with him head on ".
First Flashback In Episode Four: The Voice In The Night
But as you see in the very first flashback. We see Yokone and an older Avatar Aang, older Toph and older Sokka. Then you see a close up shot of Yokone. After that we see Avatar Aang attacking someone but we do not see who the person is.
Second Flashback In Episode Six: And The Winner Is...
In the second flashback we see Toph showing Avatar Aang something. Then we see Yokone smiling and Aang is standing right behind him. Then Yokone stands up while he is still smiling. Then Avatar Aang goes into the Avatar State for a few seconds. Last we see a close up of Avatar Aang's face which looks like it is contorited in rage.
Third Flashback In Episode Eight: When Extremes Meet
In the third flashback we see Yokone once again and then a split second later we see his face contorte into pain. Possibly someone is using the subskill bloodbending on him. Then we see Sokka in pain as well. Then it looks like Toph is trying to stop Yokone from bloodbending by metalbending while this is happending Yokone is standing up but she gets affected by the bloodbening as well. The last thing we see is Aang strugling to stop Yokone from hurting Toph and Sokka.