Grants the purple aura. While your Pokemon has this aura, move cooldowns are reduced by 10% for about 70 seconds. Defeating it grants a buff that reduces the cooldowns by about 10% of your Pokemon's moves for about 70 seconds.
Defeating Accelgor will give a 10% cooldown reduction from its boost and will help you wipe out wild Pokemon faster, allowing you to level up faster and get access to more powerful techniques faster. Pokemon with high movement speed like Junglers will definitely benefit from its effects.