Here is a Pokemon Revolution Online guide on how to get to Articuno in Seafoam Island. Note that at the moment, you cannot catch said pokemon but you can defeat it for experience points.
There are basically two entrance in Seafoam Islands – from Fuchsia and from Cinnabar. In this guide we will use the entrances which is accessible if you take the Fuchsia beach route.
Enter the cave, then the other entrance in Seafoam 1F as shown in the photo below.
You are now in Seafoam B1F, go east then go down when you see the first ladder. You do not need any HM or TM to get through this bunch of icy rocks. Just find the path as shown below.
Seafoam B2F is quite easy as you only need to go down to the available ladder as shown below.
You should be in Seafoam B3F now. The next ladder is located on the northern part of this floor. You just need to go straight north. Use surf then use the three small bridges and walk north. You will be able to see the next ladder, use it.
Upon reaching Seafoam B4F, just use surf going south. You will see a swimmer, do not worry that one will only teach a pokemon the move Icy Wind for a fee. Follow the path as you go east. Then you will see stairs going to Articuno. See the photos below.
There you go. You can leave Articuno alone or defeat it. You cannot catch it.
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