Rpg Maker Developers Group

I am currently working on a horror rpg game. Ive run into a slight snag. I have 2 characters, in different places in the game that will eventually meet back up. With that being said, I want the map to change to fit the events of the other character. What Im getting snagged on is. Actor  A will walk into a room through a door. That room has a cut scene and when the cut scene is over. Actor A will run out of the room scared. Actor A will then exit room through door and re enter previous hall. Where the ground will crumble and Actor A falls through. Actor B will hear the commotion and will head to where the ground has fallen apart. Thus cutting off the room for Actor B to get into and the tiles in front of the room become a giant hole.

So with that being said. I tried adding an event where when actor A transfers back to the hall they would touch an event and it would change the tiles and actor A would fall through. The problem Im having is that if I test play the game and actor B  touches the event it starts. I really want this event to completely hidden or non active until actor A comes out of the room and triggers it. Also I cant get the tiles to change. 

Any thoughts?

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