Shiny Articuno is just like any other shiny pokemon you have a 1 out of 8000 chance to make it appear and since Articuno is part of the map screen rather than a Random Encounter you will need to Save your game before trying to capture it then press A to fight it if it's not shiny reset the game and try again each time you open your file you have another chance at Articuno being Shiny.
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Yes there are shiny Pokemon in firered
You can catch Articuno on seafoam island whenever you don't have to beat the Pokemon League.
NO! dookie
shiny*
If you're talking about the legendary Pokemon Articuno, you have to trade it from FireRed or LeafGreen. If you're talking about Delibird, you have to trade it from FireRed.