I'm actually really tempted to let Articuno loose in UU. I never realized how bad that thing's movepool really is. Seriously, they couldn't give it Air Slash like they did for Moltres?
Yeah, Stealth Rock is really dangerous for Articuno, and basically forces the team to have a spinner if he's on it. His defenses are good, but it's just that he can't really do anything besides stall and possibly phaze with his terrible typing. Honestly, only 2 resistances (to types pokemon hardly ever attack with in UU), and the Ground immunity (removed if it Roosts too quickly) is very poor, and IMO, it overrides the guy's defenses. Having a weakness to 3 common attacking types in UU (steel isn't common enough to warrant mention), with one of them being 4x really doesn't help to compensate.
Articuno's offensive stats aren't all that bad, but then when you look at his movepool, there really isn't much to use them with. On the special side, it has Ice Beam, Hidden Power, Water Pulse, Ancientpower, Blizzard and Extrasensory. Not only does it not have double STAB on the special side, but all of its unSTAB moves are extremely low in power, very poor. On the physical side, it at least gets double STAB with Avalanche/Ice Shard, Fly/Aerial Ace/Pluck (Fly isn't bad for Pressure-stalling), U-Turn and Steel Wing as the only good mentions. As you can see, both offensive movepools are really poor.
Articuno has a very low chance of doing anything to the Rock/Steels since it really can't touch them, even with Toxic, and they can strike back on his 4x weakness to Rock with their STAB moves. Bastiodon can even Taunt Arty, forcing him to attack for very low damage while Bastiodon finishes him off.
It can't do anything to all the Water/Ice pokemon in UU such as Lapras, Dewgong, Cloyster and Walrein. They all 4x resist his main STAB, and all Articuno can do to them is Roar.
Arty's in a lot of trouble if it runs into Steelix, who can not only Taunt him, but can also end him with Stone Edge, or severely damage him with STAB Iron Head.
Hell, even Mawile gives it problems, resisting everything it can do, Taunting it, allowing Mawile to set up and Baton Pass, or to just dish out some pain with Iron Head.
Bibarel can Taunt the birdie, Super Fang to chip off enough health and then kill him with Return or Waterfall, while resisting his STAB, and not taking much from the other moves.
Froslass can Taunt Arty before he even gets the chance to Roost off any damage, and it can either go all out with attack against Articuno, or just set up Spikes in its face without fear of getting phazed.
Exploud can't even get phazed by Articuno's Roar, and thanks to its huge HP, it doesn't take a huge amount of damage from Arti's attacks, especially considering Articuno needs to invest a boatload of EVs in defenses. Exploud has Overheat and Flamethrower as well as Rock Slide to deal lots of damage to Articuno. On top of that, Exploud can also Taunt it to prevent recovery.
There's also Grumpig who will take almost nothing from Articuno's special attacks, can Taunt him, or just take advantage of Articuno's liking for Toxic and Magic Coat it back at him.
Do you guys kind of see what I'm getting at here? Articuno has good stats, but his awful movepool totally kills him, because it makes him only do the stalling job. The stalling job isn't even done particularly well, however, because of his terrible typing and the 4x Stealth Rock weakness. Pretty much any Taunter will have an easy time with him as long as they don't have a huge weakness to one of his attacks, though it doesn't have much type diversity in them anyway. It can't touch any kind of Steel type, any Water type, and if it can't phaze something out or recover its health, it's in a lot of trouble.
I personally don't think it'll be a big threat, even in UU, but this is just my opinion.
