Simple switch process, I think. After the shakes and flashes, put in a switch (like Ogre Battle). In the other maps, put an event that is started when that switch has been activated, with the events

:Change BGM-Forebonding
(and, if you want...)
:Shake every 5 seconds (or something).

Then, when you go outside and kill the Ogre (or whatever), end that switch. Simple.