Human>Beast>Undead>Phantom>Dragon>Evil
When you attack human, beast and undead might drop while human might increase. Ideally you will use three weapons: one for human and phantom, one for beast and dragon, and and one for undead and evil. The elements are similar, with Fire<>Water Earth<>Air Light<>Darkness, but any of fire, earth, air, or water might lower it's opposite, and might lower Light and Darkness too.
Here's the
Gamefaqs ultimate weapon guide, you will need to be on the second playthrough to get all the training dummies.