In the March of Cainrrase ruled by a Monarchy, 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.
Monarchy - A monarchy is a form of government in which a monarch, usually a single person, is the head of state. In most monarchies, the monarch holds their position for life and passes the responsibilities and power of the position to their children or family when they die.
Trial by combat - Fight to the death, winner is innocent