Mistmane is Hulk, Star Swirl is Iron Man, Rockhoof is Thor, Flash is Captain America, Meadowbrook is Hawkeye, Sonambula is Black widow and Celestia is fury
Personally, I would make the Pillars as one of the WW2-era superhero teams like the Justice Society or the Invaders. Flash Magnus as Cap and Rockhoof as Thor works for me, actually. But Mistmane Hulk, doh! XD
I thin Stygian should be more Venom, but as hulk can be good idea too
Edited
Edit: Nice touch with the Stark Tower in the background, btw.
Edited
“PILLARS. ONE OF US DIED TONIGHT.”
I don’t see it.
Also that was never the name of any group in the actual book.