While ms supports this, current implementation is not well made.
https://github.com/TheComputerGeek2/MagicSpells/blob/main/core/src/main/java/com/nisovin/magicspells/spells/targeted/PainSpell.java#L91-L97
it fires additional event, rather than attempting to modify edby event that would fire from craftbukkit.
Unfortunately spigot/paper api do not support damaging with custom damage cause, for now you will have to use nms.
LivingEntity#hurt
Theres ongoing pr that you might either wait for to get merged (if it ever gets merged), or use it as a reference whats needed to be done PaperMC/Paper#7423
While ms supports this, current implementation is not well made.
https://github.com/TheComputerGeek2/MagicSpells/blob/main/core/src/main/java/com/nisovin/magicspells/spells/targeted/PainSpell.java#L91-L97
it fires additional event, rather than attempting to modify edby event that would fire from craftbukkit.
Unfortunately spigot/paper api do not support damaging with custom damage cause, for now you will have to use nms.
LivingEntity#hurt
Theres ongoing pr that you might either wait for to get merged (if it ever gets merged), or use it as a reference whats needed to be done PaperMC/Paper#7423