found a boss plugin on an youtube video is EpicBosses and is a boss customisable in-game ( there a GUI in-game into that , we can add skills , add armor , weapon there a big possibility and very easy to use , they support 1.15 . 1.14 , 1.13 , 1.12 , 1.11 , 1.10 , 1.9 and 1.8 )
you can create your own skill in config .
but there is everything that allows to create bosses without touching it in the config . a way to use directly after installing the plugins, while on other plugins we must try to create a boss for hours.
the link of the plugins : https://songoda.com/marketplace/product/epicbosses-the-ultimate-bosses-plugin.19