Gliscor + Defense or + Special Defense nature, - Special attack.
Max out evs in HP and the nature you decide to boost depending on if you want to make gliscor more versatile or devote him almost entirely to the physical side which will make him almost impossible to stop with physical damage but leave it completely open to special.
Toxic heal for the ability. Toxic orb for the item.
Finally for moves ( I swear its not a troll post, this set works although its frowned upon almost always. ) Protect Toxic Substitute Dig ( Yes dig )
Its all about coming in to scout out what the opponent is gonna do, crippling opponents where you can and stalling them for healing and toxic damage. Dig adds a way to attack that helps with stalling. Its got a pretty bad negative to it but it can work if your smart about it. Watch out for stuff like Gengar who you wont be able to touch, Weezing, ice types, taunt users ect.
It has pretty notable weaknesses but if used at the right time, your opponent will be raging at you in a second because they do not have any idea how to stop it while their health just burns away.
" Don't curse the darkness--light a candle! When freaky aliens give you lemons, make freaky alien lemonade. "