Rather than take on the imps right away, there is another beach you can swim/fly to with black ring members on it, behind some anti-dragon shields and defenses (which you can ignore in human form).
Did you summon your creature to help with the imps? Unless you are a few levels lower than 21, you shouldn't have too much trouble with them.
In your inventory you have the dragon stone, which will let you teleport to the battle tower (or between platforms) and back, as well as a dragon morph stone, which lets you change back and forth between human and dragon (assuming there is enough room around and above you).
You can not change into a dragon in the tower; you need to teleport to the shrine outside, jump up the rocks and run over to where there are no overhanging tree branches (IIRC you may also be able to find a spot on the path down to transform, or jump off and turn into a dragon before you get too deep into the poison gas). In the fjords, try jumping off the mountain or swimming away from land to transform, until you get a feel for how much room you need.
If you fly out over the water from the start of the fjords, you should see a bunker high in the mountains behind some anti-dragon shields and defenses. That is where you need to get to lower the barrier and disable the shields (there are a couple traders in there, as well, after they surrender).
You can either use a teleporter to get up there (the Camp Sentinel View teleporter, on the west side of the island in the middle of the channel, will bring you to Camp Eagle's Nest, where you can access the bunker) or it is also possible to fly above the anti-dragon shield and drop down in human form, if you find the right spot. The teleporter by the blind philosopher will be activated once you disable the barrier.
