You have to have rotom of course and have already gone to the kanto region.. Go to the silph co. in Saffron City. You will see the elevator will not work NO MATTER WHAT YOU TRY. Except.. If you have rotom walking with you.Go inside and Rotom will power the elevator it says. I think. The room you enter will be just like the room you get into if you got the secret key in Pokemon Platinum. Also.. The fire one will teach you overheat.. And thats the only move you can learn from the plate thingys.
As you can see, some people may have already told you you can get Hoenn and Kanto starters. WELL.. They're right. All you have to do to do this is to beat red and stuff.. Yeah. After you did all that poop, go to professors oaks lab in Pallet Town. There he'll say a bunch of stuff and you get to chose charmander, bulbasaur and squirtle. Now for Hoenn. To get Hoenn starters you have to beat Red yeah. Then go to the counter thing at the silph co. There is this guy there that you saw before (i think) if you got latios. Talk to him.. He says a whole bunch of stuff. Then he says chose a red, green or blue stone. Chose blue for mudkip. Chose red for torchick and green for treecko.
So thats all I have to say :D