There's a super Q coming up in my local (ish) area, and I can't get past AoA Magneto. I guess it's the free actions that just fascinate me. I don't get to play or playtest as much as I want because life just gets in the way sometimes so I come to everyone for their thoughts. My original thought is
Mags 150
Pixie 75
Sunfire 55 with the prime
Brimstone 20 or Atom 15 to become an Xman. If I use atom I can play an ID card.

I get +4 to map roll and would ideally use the wizkids office with all of the walls that magneto can destroy. Another version for goes theme and uses vanisher but that idea isn't nearly as fleshed out.

You need the theme team with mags to guarentee map. That is for sure. One problem that I see with mags is he only has a ten attack, and with pandora's boxes running around (which you will see a lot of) that ten attack won't be hitting anything. The theme team prob will help with that as well as the perplex, but that won't gaurentee you can hit a 20 defense (18 plus 2). I personally like using nighthawk prime with mags. He also gives you outwit which could be very vaulable in getting rid of defensive abilities for mags. Also, nighthawk nerfs krang teams pretty hard losing their bonus which you will most likely see. Then, you can also get two id cards (i recommend superman for the super strength shifting superman or wonder woman for KC wonderwoman 13 AV). I personally feel that the sunfire is good, but there might be better options. Other Mags teams I have seen run use him with Klarion and stuff so that you get prob, another perplex and some more range penetrating damage which is always good. I guess those are my thoughts on mags.

So Basically with Mags, I would go with either:
150 Magneto
75 Pixie
65 Nighthawk
5 ID Card
5 ID Card
300

150 Magneto
75 Pixie
70 Klarion
5 ID Card
300

I like the idea of using Pixie. To reduce the impact of enemy Pandora's Box, instead of using 65 points on Nighthawk, you could pick the X-Men:Gold ATA.

I'd go something like

X-MEN THEME TEAM
Magneto 150
Pixie 75
Peggy Carter 60
3x X-Men: Gold ATA 12
= 297


X-MEN THEME TEAM
Magneto 150
Pixie 75
Harley Quinn 50 / Jean Grey 50 / LE Professor X 50
ID cards SHIELD Level 7 (Nick Fury), Triathlon (3D-Man) 10
3x X-Men: Gold ATA 12
= 297


X-MEN THEME TEAM
Magneto 150
Pixie 75
Ultron-6 Drone 30
Pandora's Box w/ Sloth relic 16
ID cards SHIELD Level 7 (Nick Fury), Triathlon (3D-Man), Batman (tw Batman 150) 15
3x X-Men: Gold ATA 12
= 298
(or maybe swap a ID card for Wrath relic on Pixie. Or maybe swap Pandora's Box for The Atom)

Thanks for the feedback. I was essentially considering magneto a 12 instead of 10 because of pixies perplex and smoke cloud. Using nighthawk makes that even stronger and allows me to gamble by modifying my damage if I choose to do so.

My ID selection is somewhat limited. I have a fair amount but don't have access to level 7. My thoughts for ID characters were the 135 pt green arrow and original avengers Iron Man at 150. Both of those buff my range ability.

An idea I've been toying with:

Force Build 8684733 0
Set	#	Name	Team	Pts	Value
UXM	062	Magneto		150	SELL
UXM	051	Iceman		110	SELL
SMWW	G001P	The Atom		15	SELL
ATA	116	X-Men: Gold		4	SELL
ATA	116	X-Men: Gold		4	SELL
ATA	116	X-Men: Gold		4	SELL
WKM	MVID-008	Shang-Chi		5	SELL
NFAOS	NFID-007	S.H.I.E.L.D. Level 7		5	SELL
Force Total:				297	$0.00

Sideline

Force Build 8684733 1
Set	#	Name	Team	Pts	Value
WKM	M16-011	Shang-Chi		76	SELL
NFAOS	056	Nick Fury		120	SELL
Force Total:				196	$0.00

The Gold ATA gives you an Outsiders TA-like effect and is a more situational / budget replacement for Prime Nighthawk.

OP LE Shang can be brought in with Iceman on his Defensive Stance mode to Poison, then switches to Offensive Stance to perform his Mega-Flurry. Iceman can Sidestep and attack to lock down a character with an Ice Block on the same turn, carrying Shang out of harm's way.

Atom can move a total of 6 squares (Sidestep + 4) to get Magneto into position to attack with his scrap metal objects. Or, he stays at home until called upon to Colossal Retaliate.

You can swap out the S.H.I.E.L.D. Level 7 to a Rick Jones ID to bring in OP LE A-Bomb (using Magneto) for a Charge + Flurry attack and token effect. If you expect The Quinjet to appear, drop the ATA and add more ID Cards that give you the option to Charge + Flurry (Triathlon, OP LE Nightwing, etc.).

For any competitive build, unless you understand every nuance of your team, don't use it! Playtest until you drop! Most importantly, live, learn and have fun!