At this point, a rival 6-on-6 fight will likely involve a somewhat, extremely different set up and story than a traditional League of Evil episodes from Powerpuff Girls, Fairly Odd Parents, Jimmy Neutron, et cetera.
 
Previously, the archetype employed the use of clones, parallel realities, animated shadows, Teen Titans used golems magicked by Raven’s dad and Justice League had Lex Luthor fused with Brainiac create copies from nanomachines resembling the Justice Lords.
 
I think there could be an alternative method for the mane six to fight six individuals of equal ability. At least, if they do want to put a spin on the Silver Age trope, which they have in some episodes. :3

No no no. Bad, and too stereotype idea.  
In the trash it

@Psychopomf  
I think they should be female. Cheese Sandwich has no reason to resent Pinkie Pie, though.

I agree. They all have reasons to dislike their counterparts. True, SS reformed, but someone like Discord could turn her head to take revenge on Twilight

Lightning dust isn’t evil…spitfire and her shadowbolts are evil!

@igotnopicks  
You could argue that Lightning Dust was Dash’s friend at one point as well yet she’s up there. Having been Dash’s friend at some point doesn’t effect their current status (for the better, anyway.)
 
Sunset reformed, she doesn’t even live in the same universe, on top of that I’d go so far as to say Sunset’s reformation was more believable than Trixie’s, but Sunset is the one who grabs the spot.
 
And here I thought Capitalism was evil.
 

@Muffen-Man  
I guess Flim and Flam could qualify :D

@TnAdct1  
I don’t think Trixie would be, because both Sunset Shimmer, Lightning Dust and Suri Polomare try to be better than the mane six (at ruling a school, being a leadpony and making clothes) to gain something (Twilight’s crown, a Wonderbolt membership (or however we call that) and a trophy).  
On the other hoof, Trixie doesn’t try to be better than Twilight in particular and doesn’t plan to gain anything neither. ^^’

@Muffen-Man  
No Gilda:Because she was Dash’s friend.  
No Trixie:Because she is reformed.  
No Flim and Flam:Because Capitalism.

No Gilda? No Flim and Flam? No Trixie?

@chaos15  
Oh my god. Dreams do come true. :)

@Background Pony #F3C6  
It gets better. Evil Aquaman had an eyepatch.  

I could dig this. These three are basically mane six members without friendship.
 
In the case of Sunset Shimmer though, there’s a lot of potential for some interesting characterization, especially if her reform is true, which I’m quite hoping for.

Extremely doubtable. Sunset Shimmer was reformed, just like discord.

@Psychopomf  
Stallion peasants < PC gaming mare master race. >:D

…I could see that but will the other half also have to be female or will Cheese Sandwich be allowed as Pinkie’s Rival?

Fear the flank holders of the double sun,the piercing bolt and the buttons of so many colors!

@ClownDicks  
Orange

Yeah… I’ve been replaced.

@Background Pony #F3C6  
The ’60s and ’70s is plain awesome overall. X3

@chaos15  
Robin with an evil mustache. That is just too awesome to be real.

@Renpony  
No one has seen that episode, it hasn’t aired yet.

@Background Pony #F3C6  
Becaus eeveryone needs an evil counterpart! Just ask the Super Friends.  

@Ping_chan  
Haven’t seen that episode, but I doubt that could be the case honestly

Anti-AJ: