Use the following gameshark code (79870CB095729832), and go to the grass patch just above Slateport City (just under cyclist road entrance). Walk around for ages, and instead of getting Latios (as the code should provide), you should face a pokemon that looks like th ? symbol in the pokedex, named wth multiple ?'s and at level 2. I was led to believe that it was a Slaking, as it loafed around. However when you catch it, the game will freeze before the pokedex data is added. But still, it is pretty cool.