While Discord is still pretty kid-friendly, seeing as he's just a trickster who likes mild torment than a psychopath, he still gets into some messed up stuff.

Just look at his debut and only time as an actual villain. (Excluding Twilight's Kingdom.) Where he mentally and emotionally fucks up our heroines for his own sick amusement. He didn't even have to, he won the second he snatched the elements, but he just felt like it.

He gets into their heads and twists their biggest character traits, save for Fluttershy. Hell, Twilight, the main character, is broken to the point she's in tears and just gives up and wants to abandon everything. Discord didn't even work his magic on her the same way he did the others, and he comes in laughing in her face about it. Villain Discord is a bastard when he wants to be, especially for a show that's as family-friendly as MLP.

Yeah, but let's be honest, even that doesn't reaches the knees of the shit that Bill got up to.