Alright, got it.
Got it, and here's my save.
You know what's sad. When my test environment filters out the problem that I'm looking for... It's like schrodinger's cat for bugs
So it loaded fine and I simply walked out of the hole.
Edit: The fault is Bubbles

So apparently Towerfag set these up to potentially not exist. That is sloppy code but a rescue will fix that... Too bad he also didn't bother updating the Patch System so Map Updates are buggy.
Not sure where @event_id gets defined but the beginning of the Event just assumes it is.
It then tries to find a Event on the Map with that ID and get the Y position.
(The code assumes if nothing is there it will pass Nil to a variable, that is not what happens as position Y isn't part of Nil Class so it throws an Exception...)
Map 438: Gate of the Abyss
Code:
@y = $game_map.events[@event_id].y
Found in 10 Bubble Events on that Map.
While this can easily be fixed, RPG Maker likes to catch the Current Map to the Save File so it won't load Patch Data for that Map until that Map is Reloaded (Exit and Return)
Code:
begin
@y = $game_map.events[@event_id].y
rescue
puts("Event ID: 001 Bubbles")
if @event_id.is_a?(Integer)
puts("$game_map.events[@event_id]")
puts("@event_id = #{@event_id}")
puts("!!! Is Nil !!!")
end
@y = nil
end