In the Principality of Deipunti ruled by a Confederacy, a character must undergo a Trial by combat.
He has been framed by A monster or group of monsters - mind flayers, a beholder, giants, a dragon - 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.

Principality - The feudatory land, or state, ruled by a prince (monarch, technically), often ranking equally high as the duke.
Confederacy - A union of persons, parties, or states; a league.
Trial by combat - Fight to the death, winner is innocent