@Quxios Since my intro relies on a couple other plugins to work, I created a duplicate of the first two maps and removed all non-Qplugins stuff from those maps' events. I then turned off all non-Qplugins.
And I got this error:
Removed some more events from those events (changing player equipment, still got the error. Set event location, still got the error.)
Finally got it working, except I had an event looping, which kept me from being able to fight. So I give it an event page that does nothing when a switch (let's just call it switch A) is turned on, okay.
Finally works, except a) the enemy had the wrong name (user error, accidentally put <enemy:1> instead of <enemy:10>), b) it didn't have a sprite. So I go into the event, change the notetag, and see that it's set to change its sprite on a switch. This switch doesn't get turned on in the copied map. No problem, just set it to change its sprite when the "switch A" is turned on.
Boot up the game, and it throws the same error.
So maybe the problem isn't set event location, but the enemy event being told to change its sprite and behavior after a switch is turned on? (I have it set to fixed movement and a transparent sprite, since it's not supposed to appear until the tutorial battle starts, and I don't want it wandering into the arena before it's supposed to. The switch tells it "okay, the tutorial battle started, you can go fight now".)
That's my best guess, since I had it working fine until I set it to change event pages when "switch A" is turned on.