Articuno counters in Pokemon GO are fairly simple. Being that Articuno is a ice and flying Pokemon type, it is only natural that its moves have little to no effect on rock type Pokemon. Pokemon like Golem, Tyranitar, Terrakion, and Rhyperior has the advantage because since they are rock types, they are super resistance toward Articunos flying attacks.
Articuno Counters Pokemon GO: Best Way to Fight Articuno
A few more Pokemon to consider obviously are fire types. Fire always beats ice, so Pokemon like Charizard, and if possible another Legendary Pokemon named Entei will do the trick. Then finally you have your Steel-type Pokemon which have great defense and attacking against a Pokemon like Articuno as well. Metagross, Heatran, and another Legendary Pokemon known as Cobalion would serve you great in your attempt to capture the legendary Articuno.
Those are just a few examples of Pokemon that you could and may want to have on your person if you plan on going against this five-star raid boss. Articuno will be available for capture in-game for one hour a day from Sept. 18 to the 25. This will give players exactly one week to prove and see if they really have what it takes to catch 'em all.