In the March of Etterat ruled by a Magocracy, a character must undergo a Trial by combat.
He has been framed by A collusion of guilds - uses resource control for leverage - and if found guilty of Treason, his punishment will be Baleful Polymorph. The prisoner permanently changes into a small animal. One of my favourite D&D modules is Castle Amber. Wouldn’t it be a neat twist for the central garden to be the prison of several banished beings changed into the form of small animals? If the subjects fail their second saving throw, they even gain animal intelligence, in effect becoming just another creature in the garden.

March - Similar to a county, but usually a borderland, ruled over by a marquis. Usually heavily fortified due to it's strategically important position.
Magocracy - Magicians who were credited with great power often became chiefs and kings in early societies. A magocracy is a form of government in which society is ruled by such magi, wizards, or witches. The term is used in the Dungeons & Dragons role-playing game and other works, by analogy with aristocracy, meritocracy, and theocracy.
Trial by combat - Fight to the death, winner is innocent