You will have to trade from Fire Red or leaf Green... Just like Latias and Latios in Sapphire and Ruby, Entai, Suicune, And Raikou only appear randomly in the wild After you beat the Pokemon League. Hope This Helped, If not, then you'll have to use a Game shark or Action Replay.
Yes
no
Any pokéball
entai- legendary dog Pokemon
You have to use palpark from a GBA game(pokemon)
to get entei in crystal you need to prepare and you could find him
you catch it by chasing it use block or meanlook if it don't run attack it then thry throwing the pokeballs you have
After you go to burned tower it will appear in the wild randomly. how you catch it is up to you (personally I would use a master ball)
start with bulbasaur an finish the game (includeing n dex) and done
it is impossible without using the download from other games thing
for entai and raikou they are special random encountors suicoon is a sidequest
you need to start out with bulbasaur at the start of the game, beat the game, get the rainbow pass, encounter then track entei then try to catch it.