On the first episode on Season 3 of MLP; FiM (as well as episode 2 of Season 3) There was mentioning of a form of dark Magic that was never mention during previous episodes.

Though some have mention that the magic performed by Luna is the same, but I felt that it's different. See with her magic, she uses unusual magic that only she would know, such as controlling dreams (good and bad) as well as turn those small dreams and nightmare into reality (shown in Season 2 Episode 4 "Luna Eclipsed").

This dark magic is as said, "Magic that involves when fear and hatred take hold." This was something that Princess Celestia said and show to Twilight when she ask Twilight to help in restoring the Crystal Empire. Showing Twilight this magic, her eyes and horn gets enveloped in a purple, green, and black array of bubbling colors. And make dark crystals that started to spread. Later Twilight did that same thing (only a weaker state), mentioning to Spike that it "was a little trick that Princess Celestia taught me", yet, even though Celestia only done it once just to show Twilight the effect of this magic. At around that time, they showed that King Sombra was performing the same kind of magic (only this time the colors were black and gray).

Now that I was able to mention a part of what I saw involving the dark magic, the part I wanted to discuss about is whether or not anyone here thinks that this magic might been shown again? I mean that right after the episode, there was no mention of that form of dark magic. I know that the Crystal Empire was suppose to be the light that banishes the darkness in each other's hearts, but why mention about the, what I call a neat power, and then toss it aside. Does anyone wonder if the dark magic might be introduce again in Season 4?