Pokemon Emerald was released in 2005 for the Nintendo Game Boy Advance System. It was the second best selling video game of 2005, and the third best selling game for the Game Boy Advance during its active lifespan. Pokemon Emerald features approximately 100 more Pokemon than its predecessors, Pokemon Crystal and Gold. One of the new Pokemon is Gligar and its evolved form Gliscor.
Catch a Gligar. Gligar can be found in mountains and dark forests in Pokemon Emerald. Use your current Pokemon to get the encountered Gligar down to 25% health, then use a regular Poke-ball to catch Gligar.
Acquire a Razor Fang. A Razor Fang cannot be bought in Pokemon Emerald, but can be found on Route 244 off of the right hand side of the road. A Razor Fang can also be found by completing the Battle Tower sequence.
Make your captured Gligar hold the Razor Fang using the in game Menu option.
Use the Rest option in the in game Menu. Set the timer to night time.
Watch as your Gligar evolves into Gliscor once you finish your rest period.
Remember to make Gligar hold the Razor Fang, otherwise he won't evolve.
Do not battle with your Gligar, or he may not have enough health to be conscious. Pokemon need to be healthy to evolve.