Question: is acnologia a dragon slayer?
Answer: Acnologia (アクノロギア Akunorogia), also known as The Black Dragon (黒龍 Kokuryū) and fearsomely reputed as The Dragon King, was a cataclysmically powerful Dragon Slayer that can take the form of a Dragon at any time due from his overuse of Dragon Slayer Magic and bathing in the blood of the Dragons he killed.