I was pretty specific but I'll explain.
I have a script for VX created by me and some friends where you can re-create any event on any map when the script command is called. In a game I am making, enemies can re-create events which are projectiles using:
$game_map.events['number']
as the starting location. If I replace 'number' with @event_id then I can copy-paste the calling event without editing the event. The problem is, when you select Custom Move Type and call the script from there, @event_id becomes nil. The reason why I am using the Custom Move Type and not Parallel Process is not only to limit event lag but also because if the monster "shooting fireballs" touches you, you get injured.
Was this explanation good enough? I think I said it all exactly.