Against Others:
They are punished in the Phlegethon, a boiling, tar-like river. Guarded by demons who will stab them with pitchforks and torchure them should they come out,
they stay underwater, surfacing for air like frogs.

Against Self:
These people are those who took their own life for granted, committing suicide. They are now in the form of trees, immobile and never again to have their bodies.
On Judgement Day, their bodies will be hung from one of their limbs. Their branches, like arms, are torn off by large birds who fly through the Forest of Suicides.

Against God/Nature/Art:
These sinners walk on a burning sand. Nature strikes back, scalding their feet.

Minotaur:
The Minotaur is the quintessinal representation of Violence. He was born of the violent sodomic union between his mother the Moon Goddess and one of Poseidon's (the sea god's) beasts—a white bull.
In mythology, he was a bloodthirsty brute who fed on young maidens sent yearly from Athens. Here in Dante's Hell, he guards the circle of the violent. Here is the story.