Sorry to keep bugging ya'll, but...

[Ryuusei]

I'm trying to make an event where a secret passage is revealed. The script is as follows

-Branch if Event Started with Action Key
Tile Substitution: Upper Layer 001 -> 075

Else Handler

End

Whenever I go to click the event in game, the tile appears all over the map, and I read the tutorial stating that if I wanted to do something like open a door, I'd need to use it with a conditional branch. I'm doing something wrong, aren't I.

[Fisherson]

Hmm you're trying to make a secret door appear that's hidden right and you're using RPG maker 2003? Here's a method I used and find universally good in RPG maker 2003

1: Event Trade: Make an even that either is invisible, I assume you know how to do that, or make a chara set using the tile as a character as a Fixed Graphic. Now go to your code and look for "Trade Event Locations" and
set it so it says First Event: Tile Chara and Second Event Door or whatever you want it to be.

[daoman89]

The way I would do it is have a switch that makes the door appear once you complete the task that allows it to appear.
 
But if you're not using a door and just having an extra passage I would just make a duplicate map with the new passage way.  So map 1 would not have it and map 2 would have the passage way.  A simple fade out for .5 sec, teleport to passage map and fade back in would do the trick. 

[Prpl_Mage]

If this is an object that is supposed to dissappear when you click on it simply do this:

Event, same layer as hero, action key (give it the graphic of whatever walllike structure it's supposed to have)
Commands:
erase event.

This means that the moment you click it, it will disappear. It will have to be repeated everytime you enter the map unless you add a switch into the mix though.

In which case it would be something like this:
page 1:
Event, same layer as hero, action key (walllike graphic)
Commands:
turn switch: 0001 ON

page 2:
event, below hero, touched by hero (no graphic / open door)
remember to set the precondition to be "Switch; 0001 is ON

this will make it so that the door will appear and be in the way until the switch is on, if the switch is on - the door will not be there.
You could also do this only make the first page a switch or a lever somewhere. Of course, you need to have a page 1 of the "door" as well, only remove the command.