I heard about but what is it.
Sky Drop glitch This glitch can only occur in Double and Triple Battles. It is activated when Gravity is used while two Pokémon are in the semi-invulnerable state after Sky Drop is used. Gravity will bring the user of Sky Drop down while the target will be stuck in the semi-invulnerable state, unable to move until it is knocked out. -Thy Mewderator
Source: http://pokemondb.net/pokebase/95844/where-do-i-find-glitch-pokemon-and-how-rarely-will-it-appear?show=95913#a95913
The glitch is activated when Gravity is used while two Pokémon are in the semi-invulnerable state after Sky Drop is used. Gravity will bring the user of Sky Drop down while the target will be stuck in the semi-invulnerable state, unable to move until the user of Sky Drop is knocked out or switched out. - Bulbapedia
Source
Here. That tells you all about the glitch.