Pravuil is a Denizen who worked as a spy for Superior Saturday.
Under Mister Monday
Pravuil was a coal-collector in the Coal Cellars. He and Suzy Turquiose Blue are in a fight as Arthur finds Mister Monday to claim the key. It seems that he might be spying for a trustee.
Under Sir Thursday
Pravuil reappears as Major Pravuil and delivers the unprecedented orders to simultaneously open all 4 gates between the void and the edge of the great maze, allowing in the Piper's army of Newniths. It is likely this order did not come from Sir Thursday, it was probably an order from Superior Saturday in an attempt to return more parts of The House (namely the Great Maze) to Nothing.
Under Superior Saturday
Pravuil is shown to be an important figure, being addressed by name by Superior Saturday.