Wait, what? One of the coolest Gen 6 mechanics isn't allowed? 0_0
Also I should be forgiven for not knowing that cause I can't find any Gen 6 league rules.
If no Megas then: Carbink opener, Gardevoir, Sylveon, Azumarill, Clefable, and Klefki.
I'm going to put out some thoughts here on the mons of the Fairy leader.
Mega Mawile, probobly with Swords Dance and Sucker punch for OHKOs on most everything.
Gardevoir [possibly Mega] for a general strong special mon.
Klefki for Prankster shenanigans.
Possibly Carbink for hazards?
Azumarill for Talonflame countering and Huge Power Aqua jet.
Togekiss and Clefable for special attacking power. I'd be more likely to go with Clefable, as Togekiss no longer gets STAB on extremespeed, and Clefable gets Moonblast. On the other hand, Togekiss is a great counter for things like garchomp.
Florge