>The Pomeg glitch involves using a Pomeg Berry on a Pokémon whose current HP is very low. The Pomeg Berry lowers the HP EVs of a Pokémon to 100 (or lowers them by 10 if the Pokémon already has 100 EVs or below). Since every 4 EVs is equivalent to 1 HP (at level 100), the Pokémon's HP will decrease with each Pomeg Berry used, as long as the Pokémon has 4 or more EVs in HP. In this way, it is possible to lower the Pokémon's current HP to 0 (without causing it to faint) or a negative number.
All the Pomeg Berry glitch does is give you a Pokemon with 0HP that isnt fainted.
Source