https://github.com/HerculesWS/Hercules/pull/2061
before understanding this pull request, let's talk about the history of OnNPCKillEvent
History
during the time OnNPCKillEvent implement, monster only spawn on the fields and dungeon, in this syntax
** Create a permanent monster spawn:
<map name>,<x>,<y>,<xs>,<ys>%TAB%monster%TAB%<monster name>%TAB%<mob id>,<amount>,<delay1>,<delay2>
and the monsters that spawned with e