Gliscor's biggest threat is Ice Beam or some Ice type move. Taunt could stop him from setting up. So now we need a fast Pokemon (faster than Gliscor) to outspeed him and then use Taunt, and hopefully KO him with Hidden Power Ice.
Gliscor has 90 base Speed, so we need to outspeed that. Gengar time!
Gengar @ Black Sludge
EVs: 4 HP / 252 SpA / 252 Spe
Timid Nature (+Spe, -Atk)
- Hidden Power [Ice]
- Shadow Ball
Gliscor stopper. Or one of them. Taunt to stop setting up, and Hidden Power Ice to KO that Gliscor.
Basically you need a Pokemon to outspeed Gliscor and have Taunt with and an ice type move.