To whoever is based on Iron Man…
 
I love you 3000.

@PUBLIQclopAccountant  

 
Tirek, at least in G4, is most akin to brutish demonic monsters of legend like Mangog. His G1 original self, Tirac, would probably be ranked among the many demons in the Marvel comics, like Mephisto, though even he’s on a much lower level compared to those guys. Same goes for the more demon-esque EqG villains.
 
Grogar is not like Thanos at all. In G1 you could compare him with Doctor Doom at best, because at least he had his own kingdom to rule over, and many of his minions, the Troggles, didn’t mind him as their emperor. He suffered no traitors, something Doom can also claim (to an extent).
 
Starlight does share MCU Thanos’ boring motivation of equality, something that was just a bonus for the original Thanos, who was after Death’s love and approval more than anything else, so in that sense Starlight does resemble a Marvel character, just not an OG Marvel comics character.
 
Chrysalis and the Changelings resemble the Brood.
 
Cozy Glow… White Rabbit, I guess?
 
King Sombra would most likely be linked to villains that can use the Darkforce, which includes the very underrated and underestimated Spot.
 
The Dazzlings/Sirens are basic monsters of the depths that Namor’s fought a few times, if a lot less sympathetic.
 
The various monsters would be placed in the Savage lands, the many alien worlds with similar creatures or Monster Isle, with other classic Marvel monsters.
 
Trixie’s illusions wouldn’t make Mysterio proud, but he’s the closest to her in Marvel.
 
I’m forgetting about many others, but that’s all I got.

@Kiryu-Chan  
While I can totally see Rarity as Black Widow, there is an argument to be made for her to be Iron Man.  
Think of how many suits Iron Man has, if that isn’t a Rarity trait I don’t know what is. Plus out of all of the M6 Rarity is the only one with a sense for business and such, so she would be the rich one of the bunch.  
Oh, and one could defend RD as Black Widow if you consider that both are hardcore amazing without superpowerd or much tools.

I’m actually gonna peg Sunset for Iron Man.  
Similarly, Twilight for Hulk, Dash for Thor.

@Prowl  
What would other MLP villains be as Marvel characters?

@PUBLIQclopAccountant  

 
imo She’s got the ego to pull him off best :p
 
Personally my Avengers casting would probably go  
AJ - Captain America  
Twilight - Thor  
RD - Iron Man  
Rarity - Black Widow  
Fluttershy - Hulk  
Spike - Hawkeye  
Scootaloo - Spiderman  
Pinkie Pie - Ant Man  
Starlight - Dr Strange  
Sunset - Captain Marvel  
Grogar - Thanos
 
I know most of these characters aren’t even on this pic but I always have fun with these :p

@PUBLIQclopAccountant  
What about flash magnus?  

@Prowl  
Who should be Cap’n A-Mare-ica?
 
My quibble with the casting is that there’s no way that Dash is smart enough to be Tony Stark

The lack of anyone as Captain America burns my ass

Twilight Sparkle is the best Doctor Strange

Oh, snap!

Infinity horse.