I have made integration years ago to Herobrine from version 1.7.1 and I have been using "net.theprogrammersworld.herobrine.nms.entity.MobType" to detect if the killed entity has Herobrine.
It seems that MobType was removed in V2.0.3 so I need your help to find a way to check if a the dead entity is Herobrine when EntityDeathEvent is called?