EasyDuels is a plugin for spigot servers (1.12 - 1.16.x), offering a new 1v1 system for your server. It has many features allowing you to customize everything. It only allows you to have a single arena on your server. Here are some features:
More features here.
If you need support, check the wiki. Most questions you may have should be answered here. For any issue or suggestion click here. Leave a review here to support me!