Richter Strategy:
The Minotaur is a large, slow but powerful enemy. He attacks with a massive axe and can charge across the screen. His primary attacks are a horizontal swing and an overhead smash. The key is to stay close and attack his legs, then quickly backflip away when he prepares an attack. The Cross sub-weapon is incredibly effective here, as it hits him multiple times and can stun him. If you have the Holy Water, throwing it at his feet can also deal consistent damage. Avoid getting cornered, as his charge attack can be devastating. Time your whips between his attacks.
Maria Strategy:
Maria's agility is a huge advantage. Use her double jump to easily clear his axe swings and charges. Her Doves are good for consistent damage, but the Dragon sub-weapon is particularly effective due to its area-of-effect fire. Get close, unleash a Dragon, then double jump away. Her Cat can also deal good damage if you can keep it on him. Maria's Item Crash will make short work of him. Focus on hit-and-run tactics.