I have a love-hate relationship with Gliscor. When I'm using it, Gliscor is the greatest thing ever. When I'm up against it, I want to table flip.
Oh, and anything that normally runs a Eviolite set (ironically)
A school gaming tournament?! Lucky~!
Everyone over here is so inept at gaming, let alone Pokemon. If there was a X/Y tournament back at my school (I'm at uni now) I'm sure everyone would turn up with three starters, two pseudos and Xerneas/Yveltal.
Thing with Leafeon is its Sp. Def in addition to the number of weaknesses Grass has makes it annoying to use at times. And now that I think about it, Glaceon is pretty meh outside of Trick Room teams as well.
Best choice for a 6th Poke is to use a Curse + Sucker Punch/Payback Umbreon. Those things can dent if they let you set up.
Vaporeon is a far superior Wish passer compared to Umbreon.
Jolteon, Espeon and Sylveon are a given.
Guts Flareon with Flare Blitz is nothing to laugh at.
I'd probably go for Glaceon in the last slot as a bulky(-ish) special attacker.
Problem with eeveelutions is a serious lack of physical sweepers. Leafeon just doesn't cut it.
Just throwing it out there that on Pokemon Essentials (what Reborn is made with), 85/85/85/85/85/85 is the max EVs for an AI's Pokemon. So it won't be as hard as you think