Topic: Pokemon Ruby/Sapphire Co-op (Plus How-To for Other Pokemon Games!)

http://www.youtube.com/user/TheMasterGamePro?feature=mhw4#p/a...
Ever wanted to play Pokemon Ruby/Sapphire with another person in the overworld? Now you can! All you need is a Gameshark or Action Replay, and the walk through walls cheat.

By talking to the woman at the trade counter from above, you will walk out of bounds, past the door. Since you didn't enter through the door, the game doesn't have anywhere to send you to. Instead, it sends you to Petalburg City, which is the placeholder location. Because of this, you will both start out in Petalburg City rather than the link room. You can explore anywhere outside (you can't enter doors), and you can even walk on water!

Unfortunately, the game isn't server based, so the games aren't always synced (the NPCs randomly walk around, you may not have picked up some items, etc.). You also can't use HM's (although I heard that you may be able to get past this with a GS or AR code). Fighting alongside the other player is impossible as well. One more thing: if someone walks over an event boundary they will be frozen in place. A good example is in Petalburg City, where the guy will show you the gym if you try to leave. If you walk on the boundary and you've finished the game, you will be able to get past. If the other person hasn't finished the game, you will stop at the boundary in their game.

This trick doesn't work with any other game. However, you could use a code that allows you to change where you go when you walk through doors to replicate this trick. So... you should be able to explore the overworld in any Pokemon game.