This command will kill all monsters that were spawned with 'monster' or
'addmonster' and have a specified event label attached to them. Commonly used to
get rid of remaining quest monsters once the quest is complete.

If the label is given as "All", all monsters which have their respawn times set
to -1 (like all the monsters summoned with 'monster' or 'areamonster' script
command, and all monsters summoned with GM commands, but no other ones - that
is, all non-permanent monsters) on the specified map will be killed regardless
of the event label value.