Oaky, this team looks pretty solid, but needs a little work. I'll try to keep the changes as minimal as possible.
Ferrothorn
My only suggestion for Ferro is to change Toxic to Protect and one of Gyro Ball or Power Whip to Leech Seed. With Rocky Helmet you have no reliable recovery, so Protect + Leech Seed can help to stall out the opposition. As for the solo attack, I would keep Power Whip to deal with Rotom-W, who you have no real answer to and who checks non-Power Whip Ferro with HP Ice, Talonflme with either STAB, and Gliscor with HP Ice.
Mega Gallade
Change Rock Slide to either Knock Off, Drain Punch or Ice Punch. Knock Off is generally spammable and checks Ghost- and Psychic- types. Drain Punch provides some recovery, and Ice Punch slays Dragons and counters the likes of Gliscor and Mega Pinsir.
Gardevoir
Replace the Choice Specs with a Choice Scarf, as with Gardevoir you gereally want speed over power. Also, make her a full sweeper with 252 SpA / 252 Spe / 4 SDef. Replace Psychic with Psyshock, which allows you to target physically-weak Pokémon.
Talonflame
Roost isn't recommended on a Choice Band set. Try replacing it with Sharp Beak to keep the power boost and to play mind games with your opponent. You could try Jolly to help outspeed things, but that's a matter of personal preference.
Gliscor
No. This is not what Gliscor was meant for. Gliscor was meant for bulky Rocks setter, or even Toxic stall. This is the set I would suggest:
Gliscor@ Toxic Orb
Ability: Poison Heal
EVs: 252 HP / 252 Def / 4 SDef
Impish Nature
- Stealth Rock
- Protect
- Earthquake
- Knock Off/Roost
Stealth Rock is pretty much mandatory, and you didn't have a setter yet. Protect allows for some recovery, while E-Quake is STAB. You can either run Knock Off or Roost in the final moveslot: Knock Off to cripple the opposition or Roost for extra recovery. You could also forego both of those and use Toxic, letting you stall out with Protect + Poison Heal.
Rotom-W
Not much to complain about here, but I would suggest replacing Thunderbolt with either HP Ice or HP Fire, depending on what you need coverage for.
Overal this is a decent team, and I hope my suggestions can get you a few victories.
