Mazeppa is considered the third-strongest spitirt in the universe. He is one of the 37 transcendentalists, spirits that are more powerful or knowledgeable in one area that other scholars acn't understand what they're doing. Among the upper ranks, they're considered spirits with an obsession taken too far. But while some transcendentalists discovered omnipresence or multiverse travel, Mazeppa obsessed over death and pain. He was the spirit that discovered how to inflict pseudo-death, a special state that even an immortal could fall into. Not only that, he's the only being in the universe who can make someone feel agony while they're dead. The only reason he is 't considered the strongest spirit in the universe is because he doesn't move around a lot, preferring to act as a sort of hit man for gods.

The scariest human around would be the Grand Spiritologist of Birgammen. He's known for his experiments on weaker spirits and humans, though his are the most brutal. His goal is to become a spirit himself, wrongly assuming that will grant him immortality. So he attempts to merge spirits with humans in new ways, usually resulting in cooked remains and twisted and insane superspirits (not as strong as you might think). While it doesn't sound bad on a worldwide scale, he does have startling influence over the king of Birgammen, to the point that he controls most of the slave trade on his continent and has the power to collapse three other countries. He's been experimenting on slaves taken from other parts of the world, but is ready to expand his test group to the millions with the help of some of his twisted superspirits. The biggest issue with him is that some gods and spirits are also interested in his work, and so actually help him on occasions (I swear, all the powerful people are insane).