Articuno in depth
One, two, three
The English name is built from “Arctic” and the Spanish “uno”, and that is the joke the entire trio hangs on: Zapdos has the two and Moltres the three. It is one of the few times the Western localization built the joke around Spanish numbers rather than Latin or Greek.
The Japanese name goes in a different direction. フリーザー is “Freezer” transcribed, nothing more: in Japan, the three birds are called Freezer, Thunder and Fire, plain English loanwords that describe the element and leave it at that. The numerical joke does not exist in the original; it was invented in translation.
The 125 that used to be something else
In Generation I, Special Attack and Special Defense were not separated; there was a single Special stat. Articuno’s 125 served both to deal damage and to take it, making it a very different attacker from the one known today. Blizzard also hit nine times out of ten back then, and the Ice type barely found anything that resisted it.
Generation II’s split gave it 125 Special Defense and 95 Special Attack, and with that change it lost half of its offensive side in one go. The rest of its history follows the same direction: every generation has added more Steel and more Rock to the pool, precisely the two things that suit it worst.
The Ice bill
No other good defensive combination carries a ×4 weakness as common as Rock. Lapras shares the Ice type and its problems, but Water patches its leaks; for Articuno, Flying opens them up, because it adds weaknesses to Rock and Electric without removing any. Having one of the highest Special Defense stats of Generation I at 125 does not stop any decent Rock move from sending it off the field.
In a normal playthrough, this matters much less. It joins the team already grown, with its stats in place and an Ice move that sweeps through the late-game Dragon, Ground, Grass and Flying types. Aerial Ace and Brave Bird are on the TM list if you want to make use of its other type, although with 85 Attack the latter costs more than it delivers.
The other Articuno
The Galarian form appeared in The Crown Tundra and changed type completely: Psychic and Flying, lavender plumage, a chest marked in black and a signature move that fires psychic energy instead of ice. It keeps the same total of 580, but distributes it the other way around, towards Special Attack and Speed, and according to the official material, its temperament is cold and disdainful towards whoever stands before it. They share a silhouette and a Pokédex number, and little else: anyone looking for the old special wall will not find it in the Galarian version.