Sorry to say, but you can't catch Cloyster.
You have to catch a Shellder with a Water Stone.
You can catch a Shellder by fishing in Olivine City (SS Aqua Entrance), Vermillion City, Cinnabar Island, Seafoam Island and on Route 21.
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You can only catch Zapdos in Crystal by cheating. otherwise it is not in the game
you don't catch articuno in crystal but you can get one from red, blue or yellow.
catch it in the wild
you catch it at night
A good ice type would be whatever you want or can catch. Some of the "better" ice types would be Dewgong or Cloyster, or even an Articuno. For a complete list of ice types, go to www.serebii.net.