Ah yes, the first of the legendary birds, and the first legendary Pokemon overall. Articuno is the first legendary Pokemon most players will ever meet, most by virtue of the observation deck binoculars east of Fuchsia City in the original gen 1 games:
Sadly Articuno is the weakest of the 3 birds, and arguably the least popular despite its crisp and beautiful design. Ice/Flying is terrible defensive typing, leaves you extremely vulnerable to Stealth Rock, and doesn't have the widest movepool. But you can still run a few fun sets, and with the addition of a regional variant it has received some renewed interest these past few years.
Absolute Zero
Ability: Pressure
Item: Leftovers
Nature: Timid (+Speed -Attack)
EVs: (HP 4) (Sp.Att. 252) (Speed 252)
Moves:
Mind Reader
Sheer Cold
Hurricane
Blizzard/Roost
Set Details:
A gimmick set that turns the random chance of the 1 hit KO Sheer Cold into absolute certainty with Mind Reader. Although if your opponent switches out the 100% accuracy boost is moot, so I suppose you are still gambling. Hurricane also pairs nicely with Mind Reader and has a much higher chance of connecting if your opponent swaps out expecting a Sheer Cold. Blizzard works similarly, but if you want to focus on survivability you can sub in Roost.
Psychicuno
Ability: Competitive
Item: Life Orb
Nature: Timid (+Speed -Attack)
EVs: (HP 4) (Sp.Att. 252) (Speed 252)
Moves:
Calm Mind
Freezing Glare/Psychic/Psyshock
Air Slash
Shadow Ball
Set Details:
A straightforward boosting sweeper for the Galarian variant. Set up Calm Mind to boost power output, pick your Psychic STAB of choice depending on preference, have Air Slash be your back up STAB with added flinch support, and round out neutral coverage with Shadow Ball. Boost damage further with Life Orb, and your nature/EVs are poured into special attack and speed.
Somaticuno
Ability: Competitive
Item: Leftovers
Nature: Bold (+Defense -Attack)
EVs: (HP 252) (Defense 252) (Sp.Def. 4)
Moves:
Calm Mind
Recover
Stored Power
Air Slash/Agility
Set Details:
A Stored Power set. Get in as many Calm Minds as you can, using Recover when needed, and then unload boosted Stored Power onto your opponent. Air Slash functions as a back-up offensive option against targets that resist or block Stored Power, but if you feel confident you won't be blocked by Dark types you can sub in Agility which will solve your speed control issues all while still adding to Stored Power's base power. Leftovers keeps Articuno around longer, and a Bold nature in tangent with max EV HP and defense alongside the special defense boost of Calm Mind ensure that this arrogant bird is as sturdy as possible against opposing threats.