well first you must go to the copycat girl's house that is in saffron city. Then you have to talk to her and she will tell you she has lost her CLEFAIRY doll. Then you have to go to vermilion city and go to the Pokemon fan club. Talk to the guy beside the doll and he will give it to you. Then go outside and you will see a guy named steven. He will tell you about latias and latias will appear on your Pokemon map. (P.S latias will flee) Hope that helped :)
In pokemon Heartgold
Yes, Mewtwo, Latios and Latias will be in HeartGold and SoulSilver.
Latias is a Dragon and Psychic type pokemon.
If you mean Latias, it didn't feature in Pokemon Gold, but it did feature in HeartGold. You can find it roaming Kanto on HeartGold by using your PokeGear, there is only One Latias in the game.
You can't get to the Hoenn region in HeartGold or SoulSilver. However, Latias can be caught in HeartGold, which is a legendary from Hoenn.
The trick is to save your master ball.
You can find Latias while you're roaming Kanto in Heart Gold, and in Soul Silver you can get a Latias in Pewter City while you have the Enigma Stone.
You can't get Latios in HeartGold. You can get Latias, to get her, talk to the copycat in Saffron and find her lost doll in Vermillion city at the fan club and Steven will be out there when you come out. He will talk about Latias for a minute and Latias will be in Kanto just walking around like Raikou.
Donphan, Growlithe, Gligar, Latias, Kyogre, etc
Once you have the National PokeDex, Steven will tell you that Latias is roaming Kanto. Now you just have to find it.
after that, someone at the battle frontier will tell you about latias and latios. then, latias will start roaming kanto.
just go somewhere,anywhere