@ altodo, you're going to definitely need something with a resistance to Ice, as half your team is weak to that type. If you're not specifically going for a Fighting type, I would suggest Scizor. It would fit in well offensively along with your Gliscor and Chandelure, as it has both a good fighting move in Superpower, and powerful priority in Technician Bullet Punch, regardless of whether you decide to place a Choice Band on it or no.
It may not be the fastest Pokémon out there, but I've always been able to work around its mediocre speed by giving it a Jolly Nature + Swords Dance for those slower Pokémon that its defensive abilities shut down, and then resorting to Bullet Punch when something faster comes along.
It can also work in tandem with Cloyster, as it gets a good priority move of its own in Ice Shard, which hits a lot of offensive threats hard, and destroys others if it's needed after a Shell Smash. I've been running a set with Ice Shard, Icicle Spear, Rock Blast, and Shell Smash (along with King's Rock for maximum trolling) and the set works wonders, regardless of the item.
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@ HippowHurr, I've always found Thundurus-T to work well as a Ferrothorn counter. It heals HP from its Thunder Wave, resists both of its STABs, and 2HKO's it with Focus Blast, not counting misses. Either way you look at it, Thundurus-T completely shuts the thing down.
I've also found that Scizor can kill it, but Ferro's Thunder Wave can still cripple the bug at the wrong moment. That being said, I've run a Swords Dance with Superpower, and should the Ferrothorn stay in, you're looking at giving it a world of hurt with that move. If in the rare event you fail to kill it in a single shot (which you almost certainly will at +2), then he has other good moves at his disposal, like Bug Bite (which is very common on most Scizor sets), or even Acrobatics (which I personally run, along with a Flying Gem. However, it's not common, and not even considered standard, and perhaps even gimmicky, considering that it takes a bit of prediction skills to pull a surprise KO off successfully.)
There are other good counters out there, but those two in particular are the two that I most commonly use. Hope that helps!