Latios in our Pokedex: http://pokemon.supercheats.com/latios
REQUIREMENTS: Fix the Magnet Train
ABILITIES NEEDED: NONE
Latios [Latias in HG] will be roaming the Kanto section of the map as soon as you get the Magnet Train pass. Unlike the dogs though Latios will run BEFORE your turn if his speed is higher then yours. Routes 24 - 25 are good back and forth Routes to wait for him. Because of the pain of getting him to show up and also the fact he runs IMMEDIATELY I would use the Master Ball to just get him and get it over with. You can try to use moves like Mean Look that keep a Pokemon from running as long as your Speed is higher then Latios. If you are getting all the Legends at the end game then you probably do have him beat for Speed.
Legendary Pokemon - Latios