In the anime, before The Beasts of Maze Castle arc, when Hiei and Yusuke fight for the first time, he had a transformation called the Jaganshi form which increased his speed and power.
The only other time we see this form is in the movie Poltergeist Report.
In all the other fights (excluding The Beasts of Maze Castle, because he wasn't even breaking a sweat there): The Dark Tournament, The Chapter Black, The Demon World Tournament, he never used it again.
Is there a canonical reason for this? Or was it just forgotten about?