Iron Head is pretty much useless, most Fairies are dead to a Play Rough anyway, the only fairy that might die from it is a Togekiss, as it can live a play rough, but, why will you stay in to one anyway, unless you like Fire Blasts or that Mawile really wants to die.
Fire Fang is the way to go, as it can hit walls that would normally force her out, mainly Skarmory, which is 2HKO'ed by Fire Fang without a boost, and as long as you run some decent speed, you can outrun as long as Skarmory isn't invested in Speed.
I personally would run this once I breed a Adament Marwile
Mawile @ Mawilite
252 HP/ 150 Spd/ 102 Atk
Adament/Jolly/Impish
Play Rough
Sucker Punch
Fire Fang
Sword Dance/Rock Slide/Substitute
150 EV's in Speed means that with a Jolly nature, it hits 97 Speed at Lv 50, Based 60 Speed walls are not going first, and base 70 are going to need Speed investment to outspeed heck, even Rotom-W will need either a Timid nature or Speed Investment to outrun Mawile. With this, alot of walls are going to have to fear either getting set up on with Sword dance, or taking hard hits from Play Rough, with the Jolly nature I would run Sword Dance, as your losing quite a bit of power only getting 139 Atk after Mega Evolving, meaning a total of 278 Atk after Huge Power, you should be able to reach 300 after Huge Power with Adament however.
Sucker Punch is a must, and Fire Fang gets around Steel types, if you want to run something other than Sword Dance, Rock Slide can Surprise Fire swtich ins such as Heatran for a good 33-40% damage, Inferape is pretty much Revenge kill bait after Stealth Rock and Volcarona is pretty much as dead as a door nail.
Might not be the best set ever, and would love some views on it, but yeah, I find it a pretty good set to use