An idea to spice up duels and add content.
Let the type of AI opponent that the player faces in Duels be selectable by staff type.
This would allow the player to go on a number of different runs or challenges.
The Law run
The Chaos run
The Flyers run
The Attack run
It'd be a good way for the player to test out their builds against different staff types.
If you wanted to narrow this down you could restrict the player to using the same staff type as their opponent.
It you wanted to really open this up you could let the player go on different runs based on both their staff type and their opponents.
The law vs chaos run
The law vs flyers run
The law vs law run
The growths vs law run