As for general counters, I think skarmory/Air Balloon Heatran stops the normal physical wall Gliscor (as they carry only Earthquake and Toxic as means of damage). Generally though, almost any powerful Ice type move from a Pokemon utilizing it well IMO should knock Gliscor out cold.
Statusing it before the Toxic orb activates is another means of crippling it. As for attacking sets, anything that resists it's STABs and can tank Knock Off will fare well.
Mega Pokemon (eg - Mega Aerodactyl, Mega Gengar) would mostly do well against a Gliscor. Powerful and fast Special Pokemon take it out before it can do anything and Pokemon like Noivern would hit straight through it's substitute due to Infiltrator.
Chesto Berry Rotom-W probably deserves the special mention as it can avoid Toxic with Rest and wil take it out with Hydro Pump.
PS - Just as something I found peculiar, Boomburst Exploud blasts Gliscor to Mars O_O