all you need to do is nothing just play some other game
get a new hobby,
go to the cave that only the Pokemon master can come in to. in their u find mewtwo
After beating the Pokemon League, go to your house and look at the TV show currenty on. Identify the mystery Pokemon on TV as blue, and Latios will be anywhere in Hoenn.
you get it from oak after beating blue
bull
by beating the game
you get it from prof. oak after beating blue
ya u can trade Pokemon in blue before u beat the elite four.
If you mean temporal tower, afterwards you still have all your Pokemon (the storyline is not over)
you cant
Games: Pokemon Red Pokemon Blue Pokemon Green Anime: Pokemon League Indigo Pokemon Indigo League Pokemon Indigo Plateau
KEEP ON BEATING IT UNTIL IT JOINES YOUR TEAM!