THE REASON WHY GLISCOR IS GREAT IN OU
Gliscor @ Toxic Orb
Ability: Poison Heal
EVs: 248 HP / 188 Def / 72 Spe
- Protect / Taunt
- Roost / Taunt
- Knock Off
How too use
I'm not extremely good at explaining this kind of stuff but to keep it straight forward this set uses the old Toxic => Protect => healing move combo adding in some great natural healing every turn thanks to Poison Heal and the very annoying Knock Off which I wouldn't honestly replace by anything especially not Earthquake since this set doesn't use Swords Dance and even then you have other Pokemon who can do better usage of Earthquake you could replace Protect or even Roost with Taunt but I will cover that a bit later.
Extra annoying set great to stall and wall anything with physical damage even the hard hitting Pokemon of the OU tier.
This set is a good match-up against the like of Tyranitar which once you Knock Off his Choice Scarf, even a Jolly Nature Tyranitar gets outspeeded and is ready to be stalled. Same goes for Mega Lopunny who doesn't really carry anything to hit Gliscor especially hard because of his typing.
Mega Charizard - X could get a surprisingly hard time going through this Gliscor and breloom is pretty much checked by it unless he is Jolly to outspeed it but quite honestly most people go Adamant breloom and heavily rely on mach punch for the priority. if Altaria-Mega is going to use a Physical attacker he won't be able to get through Gliscor and Garchomp can't really take much of a bite out of Gliscor's HP every turn.
Conkeldurr probably can still hurt this Gliscor a good bit. I would presume because of how hard he can hit but I didn't get to use this set against Conkeldurr yet so I can't say for sure. Those are just a few of the high physical sweepers of this meta who can get seriously stalled by Gliscor if you play it right.
As I said earlier you can replace Protect or Roost by Taunt if you wish but this changes everything since now you are gonna turn this Gliscor into a wallbreaker / stallbreaker and a different set of EVs can get more useful there probably going something like this:
EVs: 244 HP / 192 SpD / 72 Spe
Some people seem to be liking this build but honestly I didn't try it much and from what I got results where only half decent since a lot of the Stallers / Walls in OU can get pass the little 257 SpD of Gliscor and with the fairy types using Magic Guard and Magic Bounce your better just taking away Knock Off and putting in Earthquake even though you won't hurt them much anyway especially with toxic becoming useless against them.
Taking Roost off and adding Taunt instead while keeping the first set wasn't half bad from what I experienced since predicting a switch in from a sweeper trying to get a free set up of Swords dance or Dragon Dance would allow me to Taunt them, making them unable to set up for a few turns leaving me on the other hand, able to safely enough toxic them and Knock Off their items before they could do much damage.
However, on the long term Gliscor's longevity gets pretty lowered and comes down to basically being able to take down 1 Pokemon and afflicting Toxic or Knocking Off the item of another Pokemon before falling this however played a nice roll in some of my matches and was far from useless if predicted well and kept for the later game
Gliscor definitely has its place in the OU tier being a pretty strong Physical stall / wall despite being seriously endangered when facing a Special attacker or a Weavile / Kyurem Black . Starmie is also a really bad match up for him and his usefulness kinda fall sort if you end up facing a Steel-Type like Mega Metagross and Mega Scizor to name only those two. If you are looking for a tough physical stallGgliscor is definetly worth looking at in my opinion and can be pretty useful if used properly.