these two also have an appearence together during the end credits, in both here and the end credits they seem to be friends
also moondancer was shown during the beginning of the movie as a cameo appearance. if I remember correctly, amending fences was season 5
edit: either way, I think its nice that we have new characters instead of just using current ones (outside of the mane 6) if you think about it, if somepony like discord came along the movie would probably find away for him to lose his power during it, like what happened in to where and back again, otherwise... whats the point of having a full length movie when you have discord who can end the conflict in an episode's time?