Ok in the SDCC q&a about mlp they said in season 6

You may see a return of a villain or two, but not in the way we think.

The only villain I could think of that may returned are ether Queen Chrysalis, or maybe King Sombra.
What do you they going to do with the villain in season 6.

4550544 I'm hoping to see Chwysalis and her adorable changelings again.

Given the way they wasted his potential, and his origin story, I would LOVE Sombra to have an encore and maybe even some redemption

I regard him a tragic villain that was brainwashed and his emotional turmoil, along with being lied to, served to seal his fate, and lost the pony he'd loved

Unfortunately, it's Chrysalis, Sombra is basically dead, I suppose, I hope it's Sombra!

Well, Starlight Glimmer is fairly likely to return from the premiere (she is technically a villain after all) considering how that whole incident with her ended.