Seafoam Islands (B1F)
On Route 21, between Cinnabar Island and Fuchsia City. From Cinnabar Island, surf right. A short way in, there will be a bit of sand you can step onto; do so and walk on right, taking the lower path where it splits. Once you get to the end, surf onwards to the right and then enter the cave above you. This is 1F.
If you now go down the stairs in the top left, that's B1F. Move the first rock above to the left with Strength and go up the stairs onto the platform on the left. Walk on left and down the ladder on the left end. This is B2F. Now head down the stairs on the left, go down below the ice floor and then up to slide across it, slide across the ice floor on the right, position yourself to be just above the trainer on the ice floor below below and then slide down, then to the right once you hit him. Then go down the ladder on the right to B3F.
Finally, from there, go left below the ice floor there and slide up straight into the near two ice blocks. Then go back on the right side of the ice floor and slide left into the final block and follow after it as it locks into place by the wall. From there, slide up and head left again and go down the ladder there to B4F.
Like in Red, Blue and Yellow, Articuno (level 50) resides deep within Seafoam Islands. Go to B4F as instructed above, surf down into the water below you, head right and then up, up onto the platform, off to the right and back into the water down the stairs on the right, then on down and to the right, up the stairs onto the next platform and then up the ladder there. Now go up the ladder on the left, head right over the bridge and then down the ladder, down the other ladder above, and then down into the water there. Finally, surf on to the left until you get to a large platform above you. Articuno is standing there, ready to face you.
How to read this table
The bolded horizontal headings stand for the main condition that affects the following slots; the big cells on the left side describe which circumstances must apply for the rows they span to be active. The percentages tell you the chance of a Pokémon from this slot (row) appearing for any given wild encounter, provided the condition on the left holds.
Each condition (i.e. each bolded horizontal heading) always has the same number of slots active. Usually it's two, though the radio condition in HG/SS has four slots and tables can have any number of static slots combined under one blank condition (-) for less cluttered viewing. This is reflected in the slots usually being displayed in pairs, which except for the aforementioned HG/SS radio conditions always means that only one pair is active at any one time. (For the radio conditions, it's either two pairs or one quadruple.)
If all this confuses you, and I don't blame you, just set the conditions in the form on the right to what actually applies for you right now and press the Refresh Table View button, which will hide all the inactive slots and leave only the Pokémon you're actually going to be seeing. This will also recalculate the statistics at the bottom of the table accordingly.
Walking in tall grass or a cave
|Always||20%||Seel lv. 32||Seel lv. 32|
|20%||Golbat lv. 34||Golbat lv. 34|
|Radio off||10%||Psyduck lv. 28||Psyduck lv. 28|
|10%||Seel lv. 34||Seel lv. 34|
|10%||Golbat lv. 32||Golbat lv. 32|
|10%||Golduck lv. 34||Golduck lv. 34|
|Hoenn radio||10%||Absol lv. 28||Absol lv. 28|
|10%||Absol lv. 34||Absol lv. 34|
|10%||Makuhita lv. 32||Makuhita lv. 32|
|10%||Makuhita lv. 34||Makuhita lv. 34|
|Sinnoh radio||10%||Bronzor lv. 28||Bronzor lv. 28|
|10%||Bronzor lv. 34||Bronzor lv. 34|
|10%||Chingling lv. 32||Chingling lv. 32|
|10%||Chingling lv. 34||Chingling lv. 34|
|Always||5%||Zubat lv. 29||Zubat lv. 29|
|5%||Zubat lv. 28||Zubat lv. 28|
|Always||4%||Golduck lv. 32||Golduck lv. 32|
|4%||Psyduck lv. 28||Psyduck lv. 28|
|Always||1%||Psyduck lv. 27||Psyduck lv. 27|
|1%||Psyduck lv. 26||Psyduck lv. 26|
per 100 encounters
23 Special Defense
30 Special Attack
23 Special Defense
30 Special Attack