According to an issue opened in the Paper issue tracker, an update is needed to this plugin to avoid loading issues:

The Magic plugin has an invalid plugin.yml. They are both depending on and requiring loading before MobArena and Skript. A plugin can't load after and before a plugin at the same time. Report this to the Magic plugin.

PaperMC/Paper#8867 (comment)

This should be fixed in this dev build:

https://jenkins.elmakers.com/job/MagicPlugin/4210/

I will do some testing and make an official release when I can.

Thanks for letting me know about this issue!