Ash's Gliscor was one of the Pokémons that Ash caught in Sinnoh.
Gliscor was caught as a Gligar that was afraid of heights and couldn't fly very well. Gligar was used to battle Paul's Gliscor but was no match for its evolved form and Gliscor knocked it out with Guillotine. Gary suggested to evolve Gligar with a Razor Fang into Gliscor so it can overcome these fears. Ash's Gligar eventually evolved into Gliscor and saved Ash at a canyon.
Ash used Gliscor to battle the air master's Scizor and learned Giga Impact and stayed there to train with the air master. Gliscor was seen again, but was replaced by Gible. Ash summoned Gliscor from McCann in order to battle Paul in the Sinnoh league. Gliscor had perfected Giga Impact and while training with McCann, it learned Stone Edge. During Ash's battle with Paul, Gliscor battled Ninjask but was unable to overcome Ninjask's speed and was recalled after Ninjask knocked it into the ground, causing it to become poisoned by the Toxic Spikes that was used by Paul's Drapion. Gliscor later battled Drapion and burned it using Fire Fang defeating the Ogre Scorp pokemon. However due to its exhaustion and the fact that it had been affected by Toxic Spikes, Gliscor was defeated by Paul's Electivire.
It is assumed to be at Professor Oak's Laboratory. However it is also possible that it may have returned to McCann for more training. It will reappear along with all of Ash's Pokemon in an upcoming episode of Best Wishes Season 2.