At level 15 or higher, go to the Multiquest. Click on the girl in the black, then select the quest for the Kayda Reaver. It is best to have a good ice weapon. If you encounter a Drakel Air Raider or a Drakel Captain, kill them and click on their weapon before you click "Next". Alternately, fight monsters and eventually you will encounter a Drakel Air Raider. If you are a Fighter, the third boss is a Drakel Captain.
At the main town, there is a hole that is hidden. Click to the left of the button that reads "Battle Monsters". You will be asked if you want to go down. The monsters in the hole are somewhat strong. Do not go down if you are below level 15.
Easy Health Potions:
To get 10 Health Potions, click on Twilly, then on "The Frogzard Hunter!" and do the third part of the quest. After you kill the mosquito and the Trog, the Trog will give you 10 Health Potions. You can then either complete the rest of the quest using these potions, or flee from the next battle with them.