Hello @Isgassa and @Dorade
My apologies that this issue was not previously resolved. I've moved this thread to the General Support area so we can help you both better.
Make sure you have a Pokemon with the ability Shadow Tag in your party and head to Ice Island. If you're not finding Articuno in its previously encountered place, it make have moved to a different location on the island. Look for stairs that are partially hidden under a broken archway. Continuing along the path should get you to Articuno.
You can reference images of the stairs in this thread - https://pokemonrevolution.net/forum/topic/155974-articino-on-ice-island/
Please let me know if you are able to find Articuno, or if you continue to have issues encountering it.
