The antagonists: from left to right and down.
 
1/ Spike–specifically Spike in his Berserker form, that is a future issue, just keep an eye on the fire ruby  
2/ Luna–the mastermind  
3/ Cheese Sandwich–not much is about this guy, but the main thing is that Pinkie is, shall we say tense (and that’s being pretty light). So we have to keep an eye on him. He the one with a cloak. He will be introduced a little later.  
4/ Gilda–not much said about her, other than that she is one of Rainbow Dash’s close friends prior to meeting the other Elements. Just introduced.  
5/ Changling drone–probably because he/she/it is a changling, it has the ability to pretty much intimidate anyone it so desires. You have pretty much seen her in her ‘Haze’ persona  
6/ Chris–apparently this is Chrysalis, just that he’s a male in this universe. Apparently knows about the Fire Ruby that we first learned from the Architect and Spike.  
7/ Trixie–apparently a rogue magician that has sided with Luna. Needs to be introduced in a later chapter.

I don’t know why, but after reading the artist’s description the suicide squad came into my mind.

@GLord  
@chaos15
 
Or maybe it has to do with the Triforce. Look at it again.

@GLord  
I was wandering why she was wearing so much leather.

Trixie has the millennium puzzle on her nice hat?

@the metal bronyhead  
Kinda looks like Ghost from Hitman Reborn.  
!

*is HER servant

@DarkPonySoul  
nope, is not a rule 63 Chrysalis, is his servant and spike in super form is still spike, not an oc.

@RIG  
imho it’s t63 Chrysalis (the horn necklace), Trixie, Gilda, NMM, Discord (hoodie guy), OC#1 (or Sombra trololol) and OC#2 (or Spike during his greed rampage)

three canon characters, 1 oc and three not confirmed who they are…

Hmm, interesting. According to the artist, they’re going for a ‘seven deadly sins’ theme with these antagonists, with Gilda as Wrath, Trixie as Pride, and the shadowy guy in the corner being Greed.

@the metal bronyhead  
maybe Spike?

wait is that broly in the shadow?