Things You'll Need
Instructions
Go to Jubilife City. To get to Jubilife City, walk east from Oreburgh City on Route 203, or west from Canalave City on Route 210.
Enter the Poketch headquarters in the center of Jubilife City. Speak to the manager at the front desk. He gives you the Marking Map app.
Travel to the Pal Park, located at the end of Route 221. Once inside, talk to Professor Oak. He invites you to visit him at his house.
Go to Eterna City, located to the left of Mt. Coronet. Enter Professor Oak's house and talk to him. He tells you about the trio of legendary birds. After his speech, the birds start to roam around the Sinnoh region.
Place a Wobbuffet on your team, if you have one. If not, use a Pokemon that has the Mean Look move. Wobbuffet has an ability called Shadow Tag that prevents wild Pokemon from fleeing. The Mean Look move has the same purpose.
Tap the red button on the bottom screen to change the current Poketch app. Scroll to the Marking Map app. This is a map of Sinnoh, and the locations of all three birds, including Articuno, are marked on the map.
Go to the location of one of the icons on the Marking Map. The icon may move to a new location; if so, follow it. One of the three birds appears to fight you.
Use the Mean Look move as soon as Articuno appears. If you have a Wobbuffet, Articuno is automatically prevented from running away. Damage the bird and throw your best Poke Balls at Articuno to catch it.