dumbo-the-developer/Duels ? reverse-engineered prompt

Build me a Minecraft Duels plugin that lets players challenge each other to one on one fights, plus a simple free for all mode too. I want it to be something other plugins can hook into through an API, so make the core plugin easy to depend on and keep the API clean. It should work nicely with optional WorldGuard support if that fits, and be set up as a proper server plugin with the usual plugin.yml stuff and a straightforward way for other developers to get the plugin instance.

Please make it ready to build from the repo, organized like a real multi module Java project, and include the parts needed for the main plugin, the API, and the optional integrations. If any current docs or APIs would help, look them up online and follow the expected Minecraft plugin patterns.