Gen V
Articuno @ Life Orb / Weakness Policy (Gen VI)
Ability: Pressure
Modest Nature
EVs: 252 HP / 252 SpA / 6 SpD
- Ice Beam
- Hurricane
- Roost
- Agility
Articuno's type is good offensively, and while some would want a coverage move, Articuno can manage since Ice/Flying cover each other decently, and Roost is just too good to pass up. With something as bulky as Articuno, that is. But, Articuno's defensive type is quite poor, and while its good offensively, its base Special Attack is average at best, and base 85 Speed leaves even more to be desired. A moveset with Agility lets it pump all its EVs into its bulk and fully maximize its Special Attack with a Modest Nature, thereby softening up its offensive flaw and capitalizing on its bulk. This set does really well as a Special Tank because of its sheer raw stats and access to Roost, as most Special Attackers are unable to 2HKO it without a super effective move; without it Articuno can just tank them to death at its pleasure. Agility is great in general since it gives a good feel and sweeping potential and makes its weakness a lot more manageable (Your opponent has to eat one of your STABs before they can hurt you!).
Life Orb is good for Gen V, but the Nerf to Special Attacks in Gen VI makes it even harder for Articuno to get by with 95 Base Sp. Attack, and while it also means Articuno can take Special hits better that ever could, it's fair to say that the transition was more of a Nerf than a buff. However, Weakness Policy is an interesting item for this set since it boosts its Special Attack through the roof, well beyond Gen V Life Orb (+No Recoil), and Articuno can easily use Roost to lure enemies and take a Super-effective Attack such as Fire Blast or (non-STAB) Stone Edge, although it's a rather gimmicky item as a whole. Electric type moves are extremely easy to handle since even a Life Orb Thundurus stands no chance at OHKOing with Thunderbolt, and Articuno can outspeed with Agility and Roost back its HP to decent levels. Maybe not on Thundurus, but there are many Pokemon that are weaker than Thundurus.