Maintain a medium distance from him at all times.Do this a few times and the fight is done. Use a bleed weapon with the BloodFlame enchantment, and land a 3x charged combo attack when he is sleeping to do more damage/ bleed build up than performing a critical hit would do. If he exits the cloud, a second pot will put him to sleep (doesn't work with online players summoned). If the pot is a direct hit and he stays in the cloud, 1 pot will put him to sleep. Use sleep pots with a strong spirit summon such as Lhutel the Headless +4 to bait the Apostle to provide an opening for the pot to land.
