Have you cleared down the mountain path, and swam across to another couple beaches? The toughest opponents at the start of the fjords are level 21 imps (along the path past the mine and on to High Hall and the harbour), which shouldn't be too much trouble if you summon your creature. Trying to take out a couple imps at level 17, to get to level 18 before heading to Sentinel Island, I found the creature much more helpful with a level 2 ranger head than a level 6 warrior head, and I later switched to a mage head.
I have not played a ranger yet (waiting for DKS) but many of the imps are in relatively tight groups, so exploding arrows should work well.
Did you take the teleporter to the one left outside on Sentinel Island? There should be a few opponents remaining from when you automatically returned to the battle tower (jump up the rocks by the teleporter and run over to a spot where there are no overhanging branches in order to get enough room to turn into a dragon. You can find the book what's-his-name wanted, from a ship in a tree, though you may want to read the book yourself, rather than complete the quest (can not do both). He gets mad if you talk to him after that, but you don't actually need to talk to him again for anything. There are a few other chests to loot, as well, and possibly something else of interest if you explore the area around the island.
There is a cave near the source of the higher waterfall across from the grand knight shrine, though opponents there are level 22. After exploring past 3 teleporters in that cave, taking out the boss there gave me a very nice hammer (quest item), which (along with another good hammer I found shortly after) made a significant difference in the damage I could do, and really helped take out opponents faster and easier.
