in firered and leafgreen, yes. after beating the elite four, go back to route 1.(that's where the legendary dogs are most likely to be found). have your master ball handy! run around in the grass until you find it. which legendary dog you get depends on your starter. if your starter is bulbusaur, you will find entei. charmander-suicune, and squirtle-raikou.
ruby
no delibird is not a ledgendary Pokemon
you catch it in the grass
in the grass in the grass in the grass
In Pokemon Leaf Green, you can catch Pokemon in the grass, water, or in a cave.
gardevoir and lucario
you catch them in the GRASS
You have to see grass and then go in the grass and battle. It is usually Elekid for me but try to get a Pokemon in White Forest. If there is no grass then you can't catch Elekid and other Pokemon so just try to get grass. :)
It attracts a ledendary pokemon.
You dont
trade them or catch it in grass or water or tall grass
white grass will get you a better Pokemon.